docs: document server-side rendering pipeline, response timing middleware, and Telegram pairing API

- Add comprehensive documentation for backend content rendering in AGENTS.md, detailing the new `render_content` and `render_title` Jinja globals built on mistune with media processing, emoji shortcodes, and XSS protection
- Document the `X-Response-Time` header and bottom-left render time indicator in README.md
- Update bot token pricing documentation to clarify fallback vs gateway cost headers
- Add `email_accounts` to soft-delete tables and `idx_users_role` composite index in database schema
- Implement `telegram_pairings` and `telegram_links` table creation with column migration and indexes
- Add `/profile/{username}/telegram` endpoint to docs API with request/unpair actions
- Register `TelegramService` in main.py lifespan and add `response_timing` middleware emitting `X-Response-Time` header
- Introduce `TelegramPairForm` model and `guard_public_host_sync` synchronous host validation function

tests/unit/services/jobs/deepsearch/worker.py

@@ -17,7 +17,7 @@ def _patch_pipeline(monkeypatch, pages):
     async def fake_plan(query, api_key):
         return [query, f"{query} overview"]
 
-    async def fake_search(queries):
+    async def fake_search(queries, emit=lambda frame: None):
         return [{"url": page.url, "title": page.title, "description": ""} for page in pages]
 
     async def fake_crawl(candidates, max_pages, emit, is_cached, should_stop):