Wire Flue agents to Convex persistence and agent env

- Add db.ts: a typed ConvexHttpClient-backed PersistenceAdapter implementing
  the full Flue store surface (submissions, streams, runs, attachments).
- Add app.ts: Hono server mounting Flue routing and registering the model
  provider from @code/env/agent.
- Update zopu agent to read provider config via env() and switch
  dev/build scripts to load ../../.env.

packages/agents/package.json

@@ -4,14 +4,17 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "build": "flue build",
+    "build": "bun --env-file=../../.env flue build",
     "check-types": "tsc --noEmit",
-    "dev": "flue dev",
-    "run": "flue run",
-    "run:zopu": "flue run zopu"
+    "dev": "bun --env-file=../../.env flue dev",
+    "run": "bun --env-file=../../.env flue run",
+    "run:zopu": "bun --env-file=../../.env flue run zopu"
   },
   "dependencies": {
-    "@flue/runtime": "latest"
+    "@code/env": "workspace:*",
+    "@flue/runtime": "latest",
+    "convex": "catalog:",
+    "hono": "^4.12.30"
   },
   "devDependencies": {
     "@code/config": "workspace:*",