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/app/(dashboard)/dashboard/providers/[id]/page.js

@@ -527,12 +527,12 @@ export default function ProviderDetailPage() {
     }
   };
 
-  const handleAddCustomModel = async (modelId, type = "llm", providerAliasOverride = providerStorageAlias) => {
+  const handleAddCustomModel = async (modelId, type = "llm", providerAliasOverride = providerStorageAlias, caps) => {
     try {
       const res = await fetch("/api/models/custom", {
         method: "POST",
         headers: { "Content-Type": "application/json" },
-        body: JSON.stringify({ providerAlias: providerAliasOverride, id: modelId, type }),
+        body: JSON.stringify({ providerAlias: providerAliasOverride, id: modelId, type, ...(caps ? { caps } : {}) }),
       });
       if (res.ok) {
         await fetchCustomModels();
@@ -1781,8 +1781,8 @@ export default function ProviderDetailPage() {
           isOpen={showAddCustomModel}
           providerAlias={providerStorageAlias}
           providerDisplayAlias={providerDisplayAlias}
-          onSave={async (modelId) => {
-            await handleAddCustomModel(modelId, "llm", providerStorageAlias);
+          onSave={async (modelId, caps) => {
+            await handleAddCustomModel(modelId, "llm", providerStorageAlias, caps);
             setShowAddCustomModel(false);
           }}
           onClose={() => setShowAddCustomModel(false)}