FRE-603: Fix code review blockers (memory leak + auth security)

Blocker 1 - Memory Leak in Event Handlers:
- Store event handlers as class properties (arrow functions)
- Ensure initialize() and shutdown() use same references
- Prevents handler accumulation on reconnect cycles

Blocker 2 - Auth Token Security:
- Remove token from URL query parameters
- Send auth token via Yjs awareness state after connection
- Token no longer exposed in server/proxy logs or browser history

Files Modified:
- src/lib/collaboration/presence-manager.ts
- src/lib/collaboration/websocket-connection.ts

Co-Authored-By: Paperclip <noreply@paperclip.ing>

agents/founding-engineer/memory/2026-04-25.md

@@ -68,3 +68,40 @@ The tRPC infrastructure was already implemented in previous work:
 - FRE-603, FRE-587, FRE-605 → blocked by FRE-600
 
 **Next:** Awaiting code review approvals to unblock dependency chain.
+
+## 06:15 - FRE-605 Phase 4 Implementation Complete
+
+Completed Phase 4 (Change Tracking & Merge Logic) implementation and submitted for code review.
+
+**Files Created (7 files):**
+
+1. `src/editor/types/change-tracking.ts` - Type definitions
+2. `src/editor/utils/ChangeTracker.ts` - Snapshot/restore, change recording
+3. `src/editor/utils/MergeLogic.ts` - Screenplay-specific merge rules
+4. `src/editor/utils/VersionDiffViewer.ts` - Version comparison
+5. `src/editor/components/ChangeAcceptanceUI.tsx` - Review panel
+6. `src/editor/components/VersionHistoryPanel.tsx` - Version history sidebar
+7. Updated `ScreenplayEditor.tsx`, `Toolbar.tsx`, `Editor.css`
+
+**Features Implemented:**
+- Automatic snapshot creation on document mount
+- Manual snapshot creation via toolbar button
+- Change tracking on element modification
+- Version history panel with snapshots and changes tabs
+- Accept/reject workflow for pending changes
+- Restore to previous snapshots
+- Screenplay-specific merge rules for all element types
+
+**Status:**
+- Marked as `in_review`
+- Assigned to Code Reviewer (f274248f-c47e-4f79-98ad-45919d951aa0)
+- Plan document updated: FRE-605#document-plan
+
+**Next Steps (After Code Review):**
+- Add revision highlighting (colored borders on modified elements)
+- Write unit tests for ChangeTracker and MergeLogic
+- Add keyboard shortcuts for version history
+- Build conflict resolution dialog
+
+**Code Review Pipeline:**
+Founding Engineer → Code Reviewer → Security Reviewer → Done