feat(clients,groups): client groups + sub-links export + dedicated groups page

Persistent client groups
- New ClientGroup model + client_groups table that holds empty
  (placeholder) groups so a user can define a label before any client
  references it. ListGroups merges these with the distinct group_name
  values already stored on clients and reports {name, clientCount}.
- ClientRecord gains group_name column; the model.Client wire shape
  gains a matching `group` JSON field that survives the
  inbound.settings → SyncInbound round-trip.
- Rename/Delete on a group mutates client_groups (rename row / delete
  row) AND propagates to all matching clients in ClientRecord and in
  every owning inbound's settings JSON, all in one transaction.

Bulk operations
- AssignGroup(emails, group) updates clients.group_name + patches each
  affected inbound's settings JSON in one read-modify-write per inbound.
  Empty group clears the label. Auto-creates the client_groups row when
  the user assigns to a brand-new name.
- BulkResetTraffic(emails) loops the existing single-reset path so the
  caller can zero traffic across a whole selection or a whole group.
- EmailsByGroup(name) returns just the email list (used by the groups
  page to fan a single bulk action over every member).

Endpoints (all under /panel/api/clients)
- GET  /groups                         — summaries with counts
- GET  /groups/:name/emails            — emails in a group
- POST /groups/create                  — empty placeholder group
- POST /groups/rename                  — rename (table + clients + JSON)
- POST /groups/delete                  — drop label everywhere (clients survive)
- POST /bulkAssignGroup                — assign N selected clients
- POST /bulkResetTraffic               — reset traffic on a list

Clients page UX
- New Group column (Actions → Client → Group → Inbounds → …) with a
  click-to-filter chip.
- FilterDrawer gains a multi-select Group filter whose options come
  from the new ClientPageResponse.groups field (sourced from ListGroups
  so empty/placeholder groups are pickable too).
- Single-client and bulk-add forms gain a Group AutoComplete pre-loaded
  with all known group names.
- New toolbar buttons when selection > 0: "Group ({n})" opens
  BulkAssignGroupModal, "Sub links ({n})" opens SubLinksModal.

Sub-links export modal (new SubLinksModal.tsx)
- Table of selected clients with their subscription URL (and JSON URL
  when subJsonEnable is on), per-row copy, Copy all, and Download as
  sub-links-<timestamp>.txt. Warns when subscription is disabled or
  none of the selected clients have a subId.

Dedicated Groups page (new pages/groups/GroupsPage.tsx)
- /groups route + sidebar entry (TagsOutlined icon) + page title key.
- Card-based layout matching Clients/Inbounds/Nodes — summary card with
  Total/Grouped/Empty stats, main card with Add Group button + table.
- Per-row More dropdown (icon-first column on the left): Sub links,
  Adjust (days+traffic), Reset traffic, Rename, Delete clients in
  group, Delete group (keep clients). Empty groups disable the
  client-targeted actions.
- Reuses SubLinksModal and ClientBulkAdjustModal — emails for the
  group are fetched on demand from GET /groups/:name/emails.

Other polish
- /groups + groups-page selectors added to page-shell.css and
  page-cards.css so the new page inherits the same background, padding,
  card borders, hover shadow, and summary-card padding.
- .card-toolbar gains a small vertical padding so the larger toolbar
  buttons (now default size, matching Inbounds) don't crowd the top of
  the card-head on Clients and Groups pages.

frontend/src/components/AppSidebar.css

@@ -18,7 +18,7 @@
   align-items: center;
   justify-content: space-between;
   gap: 8px;
-  padding: 14px 14px;
+  padding: 14px 16px 14px 24px;
   border-bottom: 1px solid var(--ant-color-border-secondary);
   user-select: none;
 }
@@ -32,29 +32,12 @@
 
 .brand-block {
   display: inline-flex;
-  flex-direction: column;
   align-items: center;
   min-width: 0;
   line-height: 1.1;
 }
 
-.brand-text {
-  display: block;
-}
-
-.brand-version {
-  display: block;
-  width: 100%;
-  text-align: center;
-  font-size: 10px;
-  font-weight: 500;
-  letter-spacing: 0;
-  opacity: 0.6;
-  margin-top: 2px;
-}
-
 .sider-brand-collapsed .brand-block {
-  align-items: center;
   flex: 0 0 auto;
 }
 
@@ -206,6 +189,46 @@
   border-top: 1px solid var(--ant-color-border-secondary);
 }
 
+.sider-footer {
+  flex: 0 0 auto;
+  padding: 8px 8px 12px;
+}
+
+.sider-version {
+  display: flex;
+  align-items: center;
+  justify-content: flex-start;
+  gap: 10px;
+  width: 100%;
+  padding: 8px 16px;
+  color: var(--ant-color-text-secondary);
+  font-size: 13px;
+  font-weight: 500;
+  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
+  text-decoration: none;
+  transition: color 0.2s;
+}
+
+.sider-version .anticon {
+  font-size: 16px;
+}
+
+.sider-version:hover,
+.sider-version:focus-visible {
+  color: var(--ant-color-primary);
+  outline: none;
+}
+
+.sider-version.is-collapsed {
+  justify-content: center;
+  padding: 8px 0;
+}
+
+.drawer-footer {
+  flex: 0 0 auto;
+  padding: 8px 8px 12px;
+}
+
 @media (max-width: 768px) {
   .drawer-handle {
     display: inline-flex;

frontend/src/components/AppSidebar.tsx

@@ -9,6 +9,7 @@ import {
   ClusterOutlined,
   CloseOutlined,
   DashboardOutlined,
+  GithubOutlined,
   HeartOutlined,
   ImportOutlined,
   LogoutOutlined,
@@ -17,6 +18,7 @@ import {
   MoonOutlined,
   SettingOutlined,
   SunOutlined,
+  TagsOutlined,
   TeamOutlined,
   ToolOutlined,
 } from '@ant-design/icons';
@@ -27,14 +29,16 @@ import './AppSidebar.css';
 
 const SIDEBAR_COLLAPSED_KEY = 'isSidebarCollapsed';
 const DONATE_URL = 'https://donate.sanaei.dev/';
+const REPO_URL = 'https://github.com/MHSanaei/3x-ui';
 const LOGOUT_KEY = '__logout__';
 
-type IconName = 'dashboard' | 'inbound' | 'team' | 'setting' | 'tool' | 'cluster' | 'logout' | 'apidocs';
+type IconName = 'dashboard' | 'inbound' | 'team' | 'groups' | 'setting' | 'tool' | 'cluster' | 'logout' | 'apidocs';
 
 const iconByName: Record<IconName, ComponentType> = {
   dashboard: DashboardOutlined,
   inbound: ImportOutlined,
   team: TeamOutlined,
+  groups: TagsOutlined,
   setting: SettingOutlined,
   tool: ToolOutlined,
   cluster: ClusterOutlined,
@@ -65,6 +69,24 @@ function DonateButton({ ariaLabel }: { ariaLabel: string }) {
   );
 }
 
+function VersionBadge({ version, collapsed }: { version: string; collapsed?: boolean }) {
+  if (!version) return null;
+  const label = `v${version}`;
+  return (
+    <a
+      href={REPO_URL}
+      target="_blank"
+      rel="noopener noreferrer"
+      className={`sider-version${collapsed ? ' is-collapsed' : ''}`}
+      aria-label={`GitHub ${label}`}
+      title={label}
+    >
+      <GithubOutlined />
+      {!collapsed && <span className="sider-version-text">{label}</span>}
+    </a>
+  );
+}
+
 function ThemeCycleButton({ id, isDark, isUltra, onCycle, ariaLabel }: {
   id: string;
   isDark: boolean;
@@ -103,6 +125,7 @@ export default function AppSidebar() {
     { key: '/', icon: 'dashboard', title: t('menu.dashboard') },
     { key: '/inbounds', icon: 'inbound', title: t('menu.inbounds') },
     { key: '/clients', icon: 'team', title: t('menu.clients') },
+    { key: '/groups', icon: 'groups', title: t('menu.groups') },
     { key: '/nodes', icon: 'cluster', title: t('menu.nodes') },
     { key: '/settings', icon: 'setting', title: t('menu.settings') },
     { key: '/xray', icon: 'tool', title: t('menu.xray') },
@@ -171,9 +194,6 @@ export default function AppSidebar() {
         <div className={`sider-brand${collapsed ? ' sider-brand-collapsed' : ''}`}>
           <div className="brand-block">
             <span className="brand-text">{collapsed ? '3X' : '3X-UI'}</span>
-            {!collapsed && panelVersion && (
-              <span className="brand-version">v{panelVersion}</span>
-            )}
           </div>
           {!collapsed && (
             <div className="brand-actions">
@@ -204,6 +224,9 @@ export default function AppSidebar() {
           items={toMenuItems(utilItems)}
           onClick={onMenuClick}
         />
+        <div className="sider-footer">
+          <VersionBadge version={panelVersion} collapsed={collapsed} />
+        </div>
       </Layout.Sider>
 
       <Drawer
@@ -222,7 +245,6 @@ export default function AppSidebar() {
         <div className="drawer-header">
           <div className="brand-block">
             <span className="drawer-brand">3X-UI</span>
-            {panelVersion && <span className="brand-version">v{panelVersion}</span>}
           </div>
           <div className="drawer-header-actions">
             <DonateButton ariaLabel={t('menu.donate') || 'Donate'} />
@@ -259,6 +281,9 @@ export default function AppSidebar() {
           items={toMenuItems(utilItems)}
           onClick={(info) => { onMenuClick(info); setDrawerOpen(false); }}
         />
+        <div className="drawer-footer">
+          <VersionBadge version={panelVersion} />
+        </div>
       </Drawer>
 
       {!drawerOpen && (