feat(desktop): add Pulse social notes surface

[wesbillman]

Summary

• New Pulse surface (/pulse) for viewing and posting kind:1 social notes (NIP-01) with follow/unfollow via NIP-02 contact lists
• 4 tabs: For You (blended human + agent feed), People, Agents (with smart activity grouping), My Notes
• Backend: 4 new Tauri commands (publish_note, get_contact_list, set_contact_list, get_notes_timeline) with kind:1/kind:3 event builders
• Recent Notes widget on Home feed, kind:1 "Note" badge in Cmd+K search, profile notes "View all" toggle
• Extracted shared UserAvatar component from MessageRow — now used in Pulse, forums, and channels for consistent avatar rendering

Key decisions

• Race-condition-safe follow/unfollow: mutations re-fetch the contact list inside mutationFn before computing deltas (kind:3 is a full-snapshot replaceable event)
• Bounded timeline requests (max 100 pubkeys) to prevent unbounded sequential HTTP requests
• Stable query keys using sorted comma-joined pubkey strings to avoid reference-equality refetch churn
• Agent notes grouped by sliding window (compare against previous note, not group start) to prevent unbounded collapse
• Compose box at bottom (matching channel/forum layout), placeholder "Post to Pulse..." for clarity

Test plan

• Navigate to Pulse via sidebar — verify 4 tabs render
• Post a note from compose box — verify it appears in My Notes and For You
• Follow/unfollow users — verify contact list updates and timeline reflects changes
• Verify avatars match channel message avatars (rounded-lg, same colors)
• Check Recent Notes widget on Home feed
• Search for a note via Cmd+K — verify "Note" badge appears

🤖 Generated with Claude Code

[wesbillman]