Implement conversation sharing and collaboration

[TechNickAI]

Summary

Enable sharing conversations with others - from simple view-only links to full collaborative sessions with shared context.

Specification

Full spec in knowledge/components/conversation-sharing.md

Phased Implementation

Phase 1: View Only (MVP)

• Snapshot sharing with short URLs (/s/{nanoid})
• Anonymity toggle
• Preview before sharing
• Content stripping (memory, files, tool calls)
• Revocation and share management

Phase 2: Fork

• "Continue this conversation" flow
• Copy to recipient's workspace
• Fork count tracking

Phase 3: Collaborate

• Shared context pool architecture
• Real-time participation via SSE
• Context contribution model
• Presence and typing indicators
• 20-participant limit

Phase 4: Enterprise & Polish

• Expiration, analytics, domain restrictions
• Audit trail, SCIM provisioning

Differentiation

No competitor has:

• Shared context pool with explicit contribution
• Preview before sharing
• Memory-aware sharing (context, not just transcript)

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Spawned from #423 item #18