fix(tui): show compaction progress

[kitlangton]

Summary

• track compaction as a distinct per-session activity while preserving the existing running lifecycle
• show Compacting conversation... in the prompt footer for manual and automatic compaction
• start manual progress optimistically because the blocking compact request delivers its lifecycle events together on completion
• preserve the interrupt affordance for automatic compaction and clear failed/stale phases at execution boundaries
• surface rejected /compact requests and reject duplicate/busy compactions locally

Addresses the compaction-progress portion of #32926.

Demo

compaction-indicator-final.mp4

Testing

• bun typecheck from packages/tui
• bun run test from packages/tui (202 pass, 1 skip)
• Terminal Control against a deterministic OpenAI-compatible provider: create context, run Compact session, observe live compaction status, and return to idle

[kitlangton]

Superseded by #35371, which moves manual compaction into the durable Session inbox, adds the priority barrier and queued transcript state, and builds on #35272 for streaming progress.