Consolidate env at repo root

- Move all application env vars to repository-root .env (with .env.example
  as the committed template) and drop the per-app .env.example files.
- Add @code/env subpaths (agent, convex) and consume validated exports
  everywhere instead of reading process.env directly.
- Wire every dev/build/start script to load ../../.env via bun --env-file
  and point vite.config.ts envDir at the repo root.

package.json

@@ -34,6 +34,7 @@
     "hooks:setup": "vp config",
     "dev:native": "vp run --filter native dev",
     "dev:web": "vp run --filter web dev",
+    "dev:agents": "vp run --filter @code/agents dev",
     "dev:desktop": "vp run --filter desktop dev:hmr",
     "build:desktop": "vp run --filter desktop build:stable",
     "build:desktop:canary": "vp run --filter desktop build:canary",
@@ -42,15 +43,12 @@
     "dev:setup": "vp run --filter @code/backend dev:setup",
     "dev:daemon": "vp run --filter daemon dev",
     "build:daemon": "vp run --filter daemon build",
+    "build:agents": "vp run --filter @code/agents build",
     "docs:update": "bun run scripts/update-docs.ts",
     "subtree": "bun run scripts/subtree.ts",
     "fix": "ultracite fix"
   },
-  "dependencies": {
-    "@code/env": "workspace:*",
-    "dotenv": "catalog:",
-    "zod": "catalog:"
-  },
+  "dependencies": {},
   "devDependencies": {
     "@code/config": "workspace:*",
     "@types/bun": "latest",