[Spec 0602] Incorporate second consultation feedback (Gemini, Codex, Claude)

Critical fixes:
- TextDecoder must use { stream: true } for multi-byte Unicode safety
- Review comments use WorkspaceEdit, not Tower fs.writeFileSync endpoint
- Never drop PTY frames — disconnect and reconnect via ring buffer
- WebSocket auth via control message, not query param (prevents log leaks)

Architecture changes:
- Architect editor-split opt-in with panel fallback (undocumented API risk)
- Auth key re-read from disk on 401 for rotation handling
- Workspace path traverses up to .codev/config.json root
- Shared package extraction phased (types before V1, API client after)
- Monorepo workspace prerequisite noted

New sections:
- Error Handling UX
- Extension Settings schema (6 settings)
- Default Keyboard Shortcuts
- Output Channel for diagnostics
- Promote afx open URI scheme to Critical open question

Author: amrmelsayed