tracking(desktop): coordinate Side Conversation follow-ups

## Problem

Desktop Side Conversations shipped, but the document still contains several
follow-up routes with different owners: panel registration, parent-state
visibility, durable promotion, Review actions and watching, and remote Terminal
restoration. None has a shared coordination tracker, so these documented gaps
can drift or disappear without an explicit disposition.

## Desired outcome

Use this issue as the coordination surface for the documented follow-up list.
Each independent lifecycle or authority boundary should move to its own focused
child issue before implementation. This tracker closes when every item is
shipped, explicitly rejected, or represented by a durable child tracker and the
document reflects that status.

## Checklist

- [ ] Extract the remaining surface switch into a registered tab descriptor model before third-party panel types
- [ ] Surface authoritative parent status when the main Session needs input or approval, fails, is interrupted, or completes
- [ ] Decide whether an explicit user action may promote a Side Conversation into a visible durable ordinary Session before widening write access
- [ ] If promotion is accepted, preserve lineage and workspace/permission semantics and transfer cleanup ownership atomically
- [ ] Add commit selection and hunk-level stage/unstage/revert actions to Review
- [ ] Add filesystem watching and multi-repository aggregation to Review
- [ ] Add remote-host Terminal creation and a restorable route only after Runtime can honestly reattach or recreate it across restart
- [ ] Create focused child trackers for accepted slices and keep the document synchronized

## Non-goals

- Delivering all follow-ups in one PR
- Making temporary side conversations durable by default
- Reopening completed TUI Side Conversation work
- Bypassing Runtime Host admission, Session identity, or cleanup authority
- Claiming Terminal restoration before the Runtime owns a valid reattach/recreate contract

## Documentation

- [Side Conversation](https://github.com/apache/maka/blob/main/docs/side-conversation.md)

Start with docs/side-conversation.md and compare its documented follow-up routes with the checklist here. Separate each independent lifecycle or authority boundary into a focused child tracker, then update the document so every item is shipped, rejected, or represented by a durable tracker.

Written by the indexing model from the issue text.