chore: add plan files for Phase 3 advanced features

plans/phase-3-advanced-features/PLAN.md

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+# Feature: Phase 3 — Advanced Features
+
+**Branch:** `feature/phase-3-advanced-features`
+**Base branch:** `master`
+**Created:** 2026-03-25
+**Status:** 🟡 In Progress
+**Strategy:** Big Bang
+**Mode:** Automated
+**Execution:** Orchestrator
+
+## Summary
+Add import/export, ping history sparklines, user theme overrides, PWA support, Docker/Traefik auto-discovery, quick-add bookmarklet, and multi-tab sync.
+
+## Build & Test Commands
+- **Build:** `npm run build`
+- **Test:** `npm test`
+- **Lint:** `npm run lint`
+- **Type Check:** `npm run check`
+
+## Phases
+
+- [ ] Phase 1: Import/Export [fullstack] → [subplan](./phase-1-import-export.md)
+- [ ] Phase 2: Ping History Sparklines [fullstack] → [subplan](./phase-2-sparklines.md)
+- [ ] Phase 3: User Theme Overrides [fullstack] → [subplan](./phase-3-user-themes.md)
+- [ ] Phase 4: PWA Support [frontend] → [subplan](./phase-4-pwa.md)
+- [ ] Phase 5: Auto-Discovery Docker/Traefik [backend] → [subplan](./phase-5-autodiscovery.md)
+- [ ] Phase 6: Bookmarklet & Multi-Tab Sync [fullstack] → [subplan](./phase-6-bookmarklet-sync.md)
+- [ ] Phase 7: Integration & Polish [fullstack] → [subplan](./phase-7-integration.md)
+
+## Phase Progress Log
+
+| Phase | Domain | Status | Review | Build | Committed |
+|-------|--------|--------|--------|-------|-----------|
+| Phase 1: Import/Export | fullstack | ⬜ Not Started | ⬜ | ⬜ | ⬜ |
+| Phase 2: Sparklines | fullstack | ⬜ Not Started | ⬜ | ⬜ | ⬜ |
+| Phase 3: User Themes | fullstack | ⬜ Not Started | ⬜ | ⬜ | ⬜ |
+| Phase 4: PWA | frontend | ⬜ Not Started | ⬜ | ⬜ | ⬜ |
+| Phase 5: Auto-Discovery | backend | ⬜ Not Started | ⬜ | ⬜ | ⬜ |
+| Phase 6: Bookmarklet/Sync | fullstack | ⬜ Not Started | ⬜ | ⬜ | ⬜ |
+| Phase 7: Integration | fullstack | ⬜ Not Started | ⬜ | ⬜ | ⬜ |
+
+## Final Review
+- [ ] Comprehensive code review
+- [ ] Full build passes
+- [ ] Full test suite passes
+- [ ] Merged to `master`