feat: follow other users (social graph)

[podclaude]

Objective

Allow users to follow each other and see listening activity.

Features

• Follow/unfollow users
• Following/followers lists
• Activity feed from followed users
• Privacy controls for visibility

Privacy Considerations

• Users control who can follow them
• Activity sharing is opt-in
• Block/mute functionality

Acceptance Criteria

• Design social graph schema
• Implement follow commands/events
• Create following feed
• Add privacy controls

Priority

Medium-term (3-6 months)