stage-12: Telegram bot adapter

- New src/adapters/telegram_bot.py: full Telegram adapter with python-telegram-bot v22
  - Commands: /start, /help, /clear, /status, /model, /register
  - Inline keyboards for model selection
  - Message routing through existing router.py
  - Private chat: admin-only access
  - Group chat: responds to @mentions and replies to bot
  - Security logging for unauthorized access attempts
  - Message splitting for 4096 char limit
- Updated main.py: runs Discord + Telegram bots concurrently
  - Telegram is optional (gracefully skipped if no telegram_token)
- Updated requirements.txt: added python-telegram-bot>=21.0
- Updated config.json: added telegram_channels section
- Updated cli.py doctor: telegram token check (optional)
- 37 new tests (410 total, zero failures)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cli.py

@@ -174,7 +174,14 @@ def cmd_doctor(args):
     except Exception:
         checks.append(("Ollama reachable", False))
 
-    # 10. Discord connection (bot PID running)
+    # 10. Telegram token (optional)
+    tg_token = get_secret("telegram_token")
+    if tg_token:
+        checks.append(("Telegram token in keyring", True))
+    else:
+        checks.append(("Telegram token (optional)", True))  # not required
+
+    # 11. Discord connection (bot PID running)
     pid_ok = False
     if PID_FILE.exists():
         try: