feat(dashboard): per-key model restrictions, pin header routing, combo side-panel picker

- Endpoint: per-API-key model allowlist (schema v3) enforced on chat (403)
  and /v1/models; Full-access toggle + multi-select picker in Keys UI.
- Providers: honor x-connection-id in /v1/chat/completions — pinned requests
  no longer rotate to another account on failure.
- Providers: strategy saves merge into stored enabled:false override;
  Test All groups match grid sections; 1-by-1 skips disabled connections.
- Dashboard: provider-card toggle syncs from server on failure; grid toggles
  always visible; connection rows get clear-✕ for stale error banners.
- Combo editor: on desktop (xl+) the Add-Model picker opens as a floating
  side panel beside the untouched combo popup instead of stacking on top;
  mobile keeps the full-screen overlay.
- Long API-key overflow fixed in key rows + provider model sections.

open-sse/handlers/chatCore/requestDetail.js

@@ -1,4 +1,4 @@
-import { saveRequestUsage, appendRequestLog, saveRequestDetail } from "@/lib/usageDb.js";
+import { saveRequestUsage, saveRequestDetail } from "@/lib/usageDb.js";
 import { COLORS } from "../../utils/stream.js";
 import { canonicalizeUsage } from "../../utils/usageTracking.js";