chore: add plan files for Phase 3 advanced features

plans/phase-3-advanced-features/phase-6-bookmarklet-sync.md

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+# Phase 6: Quick-Add Bookmarklet & Multi-Tab Sync
+
+**Status:** ⬜ Not Started
+**Parent plan:** [PLAN.md](./PLAN.md)
+**Domain:** fullstack
+
+## Tasks
+- [ ] Task 1: Create `src/routes/api/apps/quick-add/+server.ts` — POST endpoint that accepts URL + title, creates app with defaults
+- [ ] Task 2: Create `src/lib/components/admin/BookmarkletGenerator.svelte` — generates bookmarklet JS code with user's API token
+- [ ] Task 3: Add bookmarklet section to user settings page
+- [ ] Task 4: Create `src/lib/utils/broadcastSync.ts` — BroadcastChannel wrapper for cross-tab sync
+- [ ] Task 5: Sync theme changes across tabs (dark/light toggle, primary color)
+- [ ] Task 6: Sync board changes across tabs (new boards appear in sidebar)
+- [ ] Task 7: Add i18n translations (EN/RU)
+
+## Notes
+- Bookmarklet: `javascript:void(fetch('ORIGIN/api/apps/quick-add',{method:'POST',headers:{'Content-Type':'application/json','Authorization':'Bearer TOKEN'},body:JSON.stringify({url:location.href,name:document.title})}))`
+- BroadcastChannel: create channel 'wal-sync', post messages on theme/board changes, listen in layout
+
+## Handoff to Next Phase
+<!-- Filled in after completion -->