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>

node_modules/.vite/vitest/results.json

@@ -1 +1 @@
-{"version":"1.6.1","results":[[":server/trpc/project-router.test.ts",{"duration":42,"failed":false}]]}
+{"version":"1.6.1","results":[[":src/lib/collaboration/presence.test.ts",{"duration":17,"failed":true}]]}