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/src/pages/api-docs/endpoints.ts

@@ -562,6 +562,17 @@ export const sections: readonly Section[] = [
         body: '{\n  "emails": ["alice", "bob"],\n  "inboundIds": [7, 9]\n}',
         response: '{\n  "success": true,\n  "obj": {\n    "attached": ["alice", "bob"],\n    "skipped": ["bob"],\n    "errors": []\n  }\n}',
       },
+      {
+        method: 'POST',
+        path: '/panel/api/clients/bulkDetach',
+        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.',
+        params: [
+          { name: 'emails', in: 'body (json)', type: 'array', desc: 'Emails of existing clients to detach.' },
+          { name: 'inboundIds', in: 'body (json)', type: 'integer[]', desc: 'Inbound IDs to detach the clients from.' },
+        ],
+        body: '{\n  "emails": ["alice", "bob"],\n  "inboundIds": [7, 9]\n}',
+        response: '{\n  "success": true,\n  "obj": {\n    "detached": ["alice", "bob"],\n    "skipped": [],\n    "errors": []\n  }\n}',
+      },
       {
         method: 'POST',
         path: '/panel/api/clients/bulkResetTraffic',