Add Google Contacts integration and fix critical Windows issues

- Add People API integration with contact management tools (create, list, get)
- Fix OAuth flow: replace deprecated OOB with localhost callback
- Fix Ctrl+C handling with proper signal handlers for graceful shutdown
- Fix UTF-8 encoding in scheduled_tasks.py for Windows compatibility
- Add users/ directory to gitignore to protect personal data

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

scheduled_tasks.py

@@ -93,7 +93,7 @@ class TaskScheduler:
         # Track file modification time
         self._last_mtime = self.config_file.stat().st_mtime
 
-        with open(self.config_file) as f:
+        with open(self.config_file, encoding="utf-8") as f:
             config = yaml.safe_load(f) or {}
 
         self.tasks.clear()  # Clear existing tasks before reload
@@ -155,7 +155,7 @@ class TaskScheduler:
         }
 
         self.config_file.parent.mkdir(parents=True, exist_ok=True)
-        with open(self.config_file, "w") as f:
+        with open(self.config_file, "w", encoding="utf-8") as f:
             yaml.dump(
                 default_config, f,
                 default_flow_style=False,