feat(models): capability toggles for custom models with upsert and live caps refresh

- AddCustomModelModal lets users pick vision/reasoning caps when adding a model
- POST /api/models/custom whitelists caps to booleans
- aliasRepo.addCustomModel upserts — re-adding updates caps/name in place
- /api/models includes custom llm models with stored caps overriding the heuristic
- useModelCaps refetches on customModelChanged instead of trusting a stale cache

Co-Authored-By: Claude Code <noreply@anthropic.com>

src/shared/hooks/useModelCaps.js

@@ -59,16 +59,25 @@ export function useModelCaps() {
   const [byId, setById] = useState(() => cache?.byId || {});
 
   useEffect(() => {
-    if (cache) {
-      setByFull(cache.byFull);
-      setById(cache.byId);
-      return;
-    }
     let alive = true;
-    loadModelCaps().then((maps) => {
+    const sync = (maps) => {
       if (alive) { setByFull(maps.byFull); setById(maps.byId); }
-    });
-    return () => { alive = false; };
+    };
+    if (cache) {
+      sync(cache);
+    } else {
+      loadModelCaps().then(sync);
+    }
+    // Custom models change at runtime — drop the shared cache and refetch
+    const invalidate = () => {
+      cache = null;
+      loadModelCaps().then(sync);
+    };
+    window.addEventListener("customModelChanged", invalidate);
+    return () => {
+      alive = false;
+      window.removeEventListener("customModelChanged", invalidate);
+    };
   }, []);
 
   const getCaps = useCallback(