feat(admin): add ephemeral staging DB, read-only posts overview, and dynamic search

- Implement ephemeral staging mode (APP_ENV=staging) to isolate test/dev DB writes in /tmp
- Add read-only posts management dashboard under /guanli/posts with live links and comment counters
- Add hot re-indexing endpoint (/guanli/reindex) to refresh Markdown without restarting server
- Replace static recommended search config with dynamic frequency-based trending searches
- Remove early scaffold mockup file (dropbox/zh.md) and clean legacy mock test queries
- Add native Makefile with dev, dev-persistent, test, lint, and docker targets
- Update test suite and documentation for development workflows

README.md

@@ -188,22 +188,36 @@ Post content in Chinese...
 
 ---
 
-## 8. Development & Deployment
+## 8. Development & Makefile Workflows
 
-### Run Locally
+The platform includes a native `Makefile` designed to protect your production data while developing and testing:
 
 ```bash
 # 1. Install dependencies
 npm install
 
-# 2. Run automated test suite (6/6 suites)
-npm test
+# 2. Run local development in Safe Ephemeral Staging Mode (Default)
+make dev
+# -> Copies site.db to a temp file in /tmp so your real database is NEVER mutated.
+# -> Discards all test queries and mock comments automatically on exit.
 
-# 3. Start local development server (uses ./sample-content by default)
-npm start
-# Server runs at http://localhost:3000
+# 3. Run development in Persistent Mode (only when you intentionally want to save changes to site.db)
+make dev-persistent
+
+# 4. Run automated test suite (in isolated temp DB)
+make test
+
+# 5. Run project linter
+make lint
+
+# 6. Clean temporary staging artifacts
+make clean
 ```
 
+### Database Isolation Architecture
+- **Safe by Default**: Running `npm run dev` or `make dev` automatically runs with `APP_ENV=staging`.
+- **Ephemeral Sandbox**: In staging or test mode (`NODE_ENV=test`), `server/services/db.js` mirrors the real SQLite database into a temporary sandbox in `os.tmpdir()`. You get 100% full application functionality, but all writes are discarded on exit, keeping `sample-content/data/site.db` 100% pristine.
+
 ### Docker Build
 
 ```bash