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/services/accountFallback.js

@@ -26,8 +26,14 @@ export function checkFallbackError(status, errorText, backoffLevel = 0) {
     : "";
 
   for (const rule of ERROR_RULES) {
+    // Request-scoped rule: the request body itself is at fault — no cooldown,
+    // no account lock. Caller must stop rotating and surface the error.
+    if (rule.requestScoped && lowerError && lowerError.includes(rule.text)) {
+      return { shouldFallback: false, requestScoped: true, cooldownMs: 0 };
+    }
+
     // Text-based rule: match substring in error message
-    if (rule.text && lowerError && lowerError.includes(rule.text)) {
+    if (rule.text && !rule.requestScoped && lowerError && lowerError.includes(rule.text)) {
       if (rule.backoff) {
         const newLevel = Math.min(backoffLevel + 1, BACKOFF_CONFIG.maxLevel);
         return { shouldFallback: true, cooldownMs: getQuotaCooldown(newLevel), newBackoffLevel: newLevel };