chore(dev): add pnpm dev hot-reload workflow for local development

Replace full docker compose rebuild during development with:
- pnpm dev / dev:backend (air hot-reload control-plane) / dev:frontend (vite HMR) / dev:deps
- compose.dev.yaml: postgres+docker-gateway only, host port mapping (5432/8081), container control-plane disabled via profile
- scripts/dev-backend.mjs: read .env, fill dev defaults (login admin/admin123, listen :8082, 32-byte dev master key with explicit warning on invalid .env value), ensure dep containers, run air
- vite: fixed port 5173, /api proxy to local control-plane (8082)
- README: document hot-reload dev workflow

Verified: pnpm dev end-to-end (login/API/frontend/proxy 200), Go+JSX edit hot-reload, compose config --quiet, go build ./..., web tests 65 passed, npm --prefix web run build.

package.json

@@ -0,0 +1,11 @@
+{
+  "name": "creator-hub",
+  "private": true,
+  "version": "0.1.0",
+  "scripts": {
+    "dev:deps": "docker compose -f compose.yaml -f compose.dev.yaml up -d postgres docker-gateway",
+    "dev:backend": "node scripts/dev-backend.mjs",
+    "dev:frontend": "pnpm -C web run dev",
+    "dev": "node scripts/dev.mjs"
+  }
+}