feat(clients): selective bulk attach + new bulk detach

Inbounds page:
- AttachClientsModal now shows a per-client selection table (email,
  comment, enabled tag) with search and a live "selected of total"
  counter; all clients are pre-selected so the old "attach all"
  workflow stays a single OK click.
- New DetachClientsModal on the inbound row menu lets you pick which
  clients to remove from that inbound (records are kept so they can be
  re-attached later; for full removal use Delete).

Clients page:
- New "Attach (N)" bulk-action button + BulkAttachInboundsModal that
  attaches selected clients to one or more multi-user inbounds.
- New "Detach (N)" bulk-action button + BulkDetachInboundsModal that
  removes selected clients from chosen inbounds; (email, inbound) pairs
  where the client isn't attached are silently skipped.

Backend adds POST /panel/api/clients/bulkDetach, wrapping the existing
Detach service for each email and reporting per-email
detached/skipped/errors. ClientRecord rows are kept on detach to match
the single-client endpoint; bulkDel remains the path for full removal.

frontend/public/openapi.json

@@ -2968,6 +2968,67 @@
         }
       }
     },
+    "/panel/api/clients/bulkDetach": {
+      "post": {
+        "tags": [
+          "Clients"
+        ],
+        "summary": "Mirror of bulkAttach: detach many existing clients from many inbounds in one call. For each email, intersects the client's current inbounds with the requested set and detaches from those only; (email, inbound) pairs where the client is not currently attached are silently no-ops. Emails not attached to any of the requested inbounds are reported under skipped. Client records are kept even if they become orphaned — use bulkDel for full removal. Returns per-email detached/skipped/errors lists and triggers a single Xray restart if any target inbound was running.",
+        "operationId": "post_panel_api_clients_bulkDetach",
+        "requestBody": {
+          "required": true,
+          "content": {
+            "application/json": {
+              "schema": {
+                "type": "object"
+              },
+              "example": {
+                "emails": [
+                  "alice",
+                  "bob"
+                ],
+                "inboundIds": [
+                  7,
+                  9
+                ]
+              }
+            }
+          }
+        },
+        "responses": {
+          "200": {
+            "description": "Successful response",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "object",
+                  "properties": {
+                    "success": {
+                      "type": "boolean"
+                    },
+                    "msg": {
+                      "type": "string"
+                    },
+                    "obj": {}
+                  }
+                },
+                "example": {
+                  "success": true,
+                  "obj": {
+                    "detached": [
+                      "alice",
+                      "bob"
+                    ],
+                    "skipped": [],
+                    "errors": []
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/panel/api/clients/bulkResetTraffic": {
       "post": {
         "tags": [