Wire session history into KMP/mobile bridge

[yacosta738]

Context

Follow-up from #277 (session-memory-visibility). Mobile clients are currently in stub state.

Goal

Once the Rust CLI bridge is complete, wire session history display into the KMP mobile app.

Scope

• Implement session list in mobile bridge protocol
• Add session history UI in Compose Multiplatform
• Follow the same end-user scoping model (token-hashed)

Acceptance Criteria

• Mobile app shows session history via bridge
• Session switching works on mobile
• No memory content exposed to end users

[linear]

DALLAY-207