chore: repo cleanup + docs for admin API and DB schema (v1.2.8)

- remove stale docs/admin-frontend-spec.md (old Express/EJS admin), unused templates/ (SmartAdmin copy), dead scripts/sync-agents.cjs, committed dev.pid
- add docs/API.md (admin REST API reference) and docs/DATABASE.md (DB schema)
- refresh .env.example: drop stale ADMIN_PORT/SHOP_CONTAINER, add ADMIN_URL, HEALTH_PORT, DEFAULT_LANGUAGE, CHATBOT_API_*
- add npm run lint so Gitea workflows pass
- rebrand web-testing suite from APAW to telegram-shop

package.json

@@ -6,7 +6,8 @@
     "test": "vitest run",
     "test:watch": "vitest",
     "start": "node src/index.js",
-    "dev": "nodemon src/index.js"
+    "dev": "nodemon src/index.js",
+    "lint": "find src -name '*.js' -print0 | xargs -0 -n1 node --check"
   },
   "dependencies": {
     "archiver": "^7.0.1",