feat(docker-watcher): phase 13 - volumes & environment

Per-stage env var overrides with encryption for secrets.
Volume mounts with shared/isolated modes (isolated appends
/{stage}-{tag}/ to source path). Store CRUD, API endpoints,
and frontend editors for both. Env merge during deploy.

plans/docker-watcher-core/PLAN.md

@@ -35,7 +35,7 @@ A self-hosted tool that automates Docker container deployment with Nginx Proxy M
 - [x] Phase 10: Quick Deploy & Settings Pages [domain: frontend] → [subplan](./phase-10-settings-deploy.md)
 - [x] Phase 11: Frontend Embed & Real-Time Updates [domain: fullstack] → [subplan](./phase-11-embed-sse.md)
 - [x] Phase 12: Hardening [domain: backend] → [subplan](./phase-12-hardening.md)
-- [ ] Phase 13: Volumes & Environment [domain: fullstack] → [subplan](./phase-14-volumes-env.md)
+- [x] Phase 13: Volumes & Environment [domain: fullstack] → [subplan](./phase-14-volumes-env.md)
 - [ ] Phase 14: Frontend Polish & Modern UI [domain: frontend] → [subplan](./phase-13-ui-polish.md)
 
 ### Parallel Execution Notes
@@ -58,8 +58,8 @@ A self-hosted tool that automates Docker container deployment with Nginx Proxy M
 | Phase 9: Dashboard | frontend | ✅ Complete | ⬜ Pending | ⏭️ Skip (Big Bang) | ✅ |
 | Phase 10: Settings & Deploy | frontend | ✅ Complete | ⬜ Pending | ⏭️ Skip (Big Bang) | ✅ |
 | Phase 11: Embed & SSE | fullstack | ✅ Complete | ⬜ Pending | ⏭️ Skip (Big Bang) | ✅ |
-| Phase 12: Hardening | backend | ✅ Complete | ⬜ Pending | ⏭️ Skip (Big Bang) | ⬜ |
-| Phase 13: Volumes & Env | fullstack | ⬜ Not Started | ⬜ | ⏭️ Skip (Big Bang) | ⬜ |
+| Phase 12: Hardening | backend | ✅ Complete | ⬜ Pending | ⏭️ Skip (Big Bang) | ✅ |
+| Phase 13: Volumes & Env | fullstack | ✅ Complete | ⬜ Pending | ⏭️ Skip (Big Bang) | ⬜ |
 | Phase 14: UI Polish | frontend | ⬜ Not Started | ⬜ | ✅ Required (Final) | ⬜ |
 
 ## Amendment Log