Add Gmail and Google Calendar integration

Implements on-demand Google tools (not adapter) for email and calendar access via OAuth2.

Features:
- OAuth2 user consent flow with automatic token refresh
- 3 Gmail tools: send_email, read_emails, get_email
- 3 Calendar tools: read_calendar, create_calendar_event, search_calendar
- Lazy loading pattern for Google clients
- Secure token storage with file permissions
- Browser-based setup: python bot_runner.py --setup-google

Architecture:
- Tools-only approach (zero API calls when not in use)
- User-initiated actions only (no continuous polling)
- MIME message creation for emails with threading support
- HTML to text conversion for email parsing
- ISO 8601 timestamp handling for calendar events

Files added:
- google_tools/oauth_manager.py: OAuth2 flow and token management
- google_tools/gmail_client.py: Gmail API wrapper
- google_tools/calendar_client.py: Calendar API wrapper
- google_tools/utils.py: Email/MIME helpers
- config/scheduled_tasks.yaml: Example scheduled tasks config

Files modified:
- tools.py: Added 6 Google tool handlers with lazy initialization
- bot_runner.py: Added --setup-google command for OAuth authorization
- requirements.txt: Added Google API dependencies
- .gitignore: Added google_credentials.yaml and google_oauth_token.json

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

requirements.txt

@@ -17,3 +17,9 @@ slack-sdk>=3.23.0
 
 # Telegram adapter
 python-telegram-bot>=20.7
+
+# Google API dependencies (Gmail and Calendar)
+google-auth>=2.23.0
+google-auth-oauthlib>=1.1.0
+google-auth-httplib2>=0.1.1
+google-api-python-client>=2.108.0