feat: Implement global debug flag (--debug/-d) for CLI

This commit connects the previously defined but unused DEBUG_OPTION to actual
debug logging functionality. When the --debug or -d flag is passed, the CLI
now enables DEBUG level logging for all modules, providing detailed diagnostic
information.

Changes:
- Added DEBUG_OPTION to imports in cli/app.py
- Created global_options callback to configure logging when debug flag is set
- Debug logging includes timestamps and module names for easy tracing
- Flag works with all commands (e.g., cam --debug config validate)

Usage:
  cam --debug <command>     # Enable debug logging
  cam -d <command>          # Short form

Example output shows:
  - ConfigManager initialization details
  - Config location discovery and loading
  - Validation process details
  - Timestamps and module source of each debug message

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: jzhu

code_assistant_manager/cli/app.py

@@ -20,6 +20,7 @@
 from .options import (
     CONFIG_FILE_OPTION,
     CONFIG_OPTION,
+    DEBUG_OPTION,
     TOOL_ARGS_OPTION,
     VALIDATE_VERBOSE_OPTION,
 )
@@ -33,6 +34,19 @@
     add_completion=False,
 )
 
+
+@app.callback(invoke_without_command=False)
+def global_options(debug: bool = DEBUG_OPTION):
+    """Global options for the CLI application."""
+    if debug:
+        # Configure debug logging for all modules
+        logging.basicConfig(
+            level=logging.DEBUG,
+            format="%(asctime)s - %(name)s - %(levelname)s - %(message)s",
+        )
+        logger.debug("Debug logging enabled")
+
+
 # Import commands to register them with the app
 from . import commands  # noqa: F401,E402