feat(review): unify review workflows and panel targeting

[Anton-Horn]

Summary

• replace legacy diff surfaces with the Review panel and deep-link Source Control files into it
• add compact Codex-style diffs with expandable context, inline-only review comments, file stage/unstage/discard actions, and stable background refreshes
• add agent-native Review and Request changes flows with an in-panel agent picker and CLI-backed review-note commands
• introduce one canonical panel-target transaction for new placement, existing-panel selection, or both across panel types
• support creating coding agents in existing terminals and make docked consumers create sibling tabs without entering canvas selection
• remove duplicated commit and push operations from Review while retaining review-specific actions

Validation

• npm test -- --run — 3,150 passed, 45 skipped
• npm run typecheck
• npm run build
• git diff --check origin/main...HEAD