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/messages.py

@@ -177,7 +177,7 @@ def test_send_message_appears_in_thread(alice):
     page.fill("input[name='content']", msg)
     page.locator(".messages-send-btn").click()
     page.wait_for_url("**/messages**", wait_until="domcontentloaded")
-    assert page.is_visible(f".message-bubble:has-text('{msg}')")
+    page.locator(f".message-bubble:has-text('{msg}')").first.wait_for(state="visible")
 
 
 def test_messages_page_loads(alice):