[Phase 15] Add first-run and TUI controls documentation

[cosentinode]

Scope

Add user quickstart and complete controls reference for focus, navigation, staging, queue, audit, confirmation, mouse, compact layout, recovery, and clean exit.

Acceptance Criteria

• New users can launch, inspect, stage, preview, cancel, and exit.
• Every active shortcut and y/Y distinction is documented.
• Conflict controls and mouse limitations are included.
• README links the guide; assets contain no private data.

Verification

• cargo test --locked --workspace
• Manual TUI smoke
• git diff --check

Notes

Child of #17; depends on stable Phase 12 controls and Phase 14 installation.