Session Tagging with /tag Command

What: A new command to add searchable tags to your sessions for better organization and retrieval. How to use:

/tag bugfix        # Add tag to current session
/tag bugfix        # Run again to remove (toggle behavior)
/tag feature-auth  # Use descriptive names

Details:

• Tags appear after the branch name in /resume list
• Tags are searchable with / search functionality
• Running the same tag command again removes the tag (toggle)
• Evidence: c55() at line 483604, HG0() at line 491331, nh2() at line 491336