chore: align sqlite control plane architecture

- replace default Convex control-plane wording with Rust SQLite control-plane across architecture, AGENTS, Reasonix, and design docs

- retire root Convex functions source and deploy script into recycle while keeping explicit cloud/compat/sync-replica boundaries

- add control-plane migration guard/docs and keep CodeGraph refreshed after the SQLite control-plane cutover

recycle/20260522-convex-runtime-retirement/convex/auth.config.ts

@@ -0,0 +1,8 @@
+export default {
+  providers: [
+    {
+      domain: process.env.CONVEX_SITE_URL,
+      applicationID: "convex",
+    },
+  ],
+};