fix(sub): drop external Clash shadowsocks nodes the panel cannot express (#6508)

* fix(sub): gate external Clash shadowsocks links like the inbound path

clashProxyFromExternal returned as soon as it had built the ss proxy, so an
ss:// link skipped applyTransport/applySecurity: a node whose tcp/http
obfuscation Clash cannot express was emitted anyway (mihomo then opens a plain
shadowsocks stream at a server that requires the header, and the node silently
never connects), and security=tls was silently stripped. The inbound path runs
both helpers for every protocol, so the two Clash importers disagreed about the
same node.

* fix(sub): count a dropped external link in the quota header

The client email that feeds AggregateTrafficByEmails was recorded only when a
proxy came out of the link, so a node Clash cannot represent also vanished from
the Subscription-Userinfo header of every other node in the same subscription —
the header reported another client's numbers as the whole subscription's. The
inactive-link branch already counted an email without a proxy; make that
unconditional so the header describes the subscribers, not the representable
subset of their nodes.

* docs(sub): describe clashProxyFromExternal by what it does, not by protocol

The protocol list in the doc comment went stale the moment the shadowsocks
branch stopped returning early, and it restated what the switch already says.

internal/sub/clash_service.go

@@ -78,8 +78,10 @@ func (s *SubClashService) getClash(subId string, host string, legacy bool) (stri
 		if ext.Enable {
 			hasEnabledClient = true
 		}
+		// Count the client even when no proxy comes out of this link, so the
+		// quota header does not shrink because a node is unrepresentable in Clash.
+		seenEmails[ext.Email] = struct{}{}
 		if !ext.Active {
-			seenEmails[ext.Email] = struct{}{}
 			hasInactiveExternal = true
 			continue
 		}
@@ -89,7 +91,6 @@ func (s *SubClashService) getClash(subId string, host string, legacy bool) (stri
 				name = ext.Email
 			}
 			if proxy := s.clashProxyFromExternal(el.Link, name); proxy != nil {
-				seenEmails[ext.Email] = struct{}{}
 				proxies = append(proxies, proxy)
 			}
 		}