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/e2e/profile/search.py

@@ -722,11 +722,10 @@ def test_profile_back_link(alice):
     page.wait_for_url(f"{BASE_URL}/feed", wait_until="domcontentloaded")
 
 
-def test_profile_role_display(alice):
-    # alice_test is the first user -> Admin; only admins see role badges.
+def test_profile_level_display(alice):
     page, user = alice
     page.goto(f"{BASE_URL}/profile/{user['username']}", wait_until="domcontentloaded")
-    assert page.locator(".profile-role").is_visible()
+    assert page.locator(".profile-level-bar").is_visible()
 
 
 def test_profile_avatar(alice):