fix: DB backup on schema change, MCP child cleanup, codex models, usage providers OOM

- Backup DB only on real SCHEMA_VERSION change, not every app version bump
- Kill idle MCP stdio bridge children to prevent orphan process leaks
- Add getDistinctProviders to avoid loading every row JSON blob (OOM fix)
- Update codex model list (gpt-5.6 sol/terra/luna, drop 5.3 codex variants)
- Reorder Claude default models (fable first)

Co-authored-by: Cursor <cursoragent@cursor.com>

src/app/api/usage/providers/route.js

@@ -1,5 +1,5 @@
 import { NextResponse } from "next/server";
-import { getRequestDetails } from "@/lib/requestDetailsDb";
+import { getDistinctProviders } from "@/lib/requestDetailsDb";
 import { getProviderNodes } from "@/lib/localDb";
 import { AI_PROVIDERS, getProviderByAlias } from "@/shared/constants/providers";
 
@@ -9,10 +9,9 @@ import { AI_PROVIDERS, getProviderByAlias } from "@/shared/constants/providers";
  */
 export async function GET() {
   try {
-    const { details } = await getRequestDetails({ pageSize: 9999 });
-
-    // Extract unique providers
-    const providerIds = [...new Set(details.map(r => r.provider).filter(Boolean))].sort();
+    // Query DISTINCT provider column directly — avoids parsing every row's
+    // full JSON blob (can be hundreds of MB), which previously caused OOM.
+    const providerIds = await getDistinctProviders();
 
     const providerNodes = await getProviderNodes();
     const nodeMap = {};