Fix waypoint drag, host election, segment routing, debug panel

Waypoint drag:
- Use observeDeep instead of observe to detect Y.Map property changes

Host election:
- Extracted to host-election.ts with 8 unit tests
- Simple rule: lowest real client ID is always host, deterministic
- Always sets role (host or participant), no missing roles
- Filters server docs (empty awareness state) from election

BRouter routing:
- Route segment-by-segment like bikerouter.de (one request per
  waypoint pair), guarantees route passes through every waypoint
- Merge GeoJSON segments with accumulated stats
- 8 unit tests for segment merging and waypoint splitting

Awareness cleanup:
- Track client IDs per WebSocket connection
- Immediately remove awareness on WebSocket close

Debug panel:
- Visibility + expanded state persisted in localStorage
- Hotkey (Shift+Cmd+Option+T) toggles visibility
- Labels server docs as (server)
- All logic self-contained in YjsDebugPanel.tsx

User identity:
- Color and name persisted in localStorage across reloads

Tests: 32 total (16 existing + 8 host election + 8 routing)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/planner/app/components/SessionView.tsx

@@ -3,6 +3,7 @@ import { useYjs } from "~/lib/use-yjs";
 import { useRouting } from "~/lib/use-routing";
 import { ProfileSelector } from "~/components/ProfileSelector";
 import { ExportButton } from "~/components/ExportButton";
+import { YjsDebugPanel } from "~/components/YjsDebugPanel";
 
 const PlannerMap = lazy(() =>
   import("~/components/PlannerMap").then((m) => ({ default: m.PlannerMap })),
@@ -83,6 +84,7 @@ export function SessionView({ sessionId }: { sessionId: string }) {
           </Suspense>
         </aside>
       </div>
+      <YjsDebugPanel yjs={yjs} />
     </>
   );
 }