Add split export: Export Route vs Export Plan

Split button with default "Export GPX" (track only) and dropdown:
- Export Route: clean track for use in any app
- Export Plan: track + waypoints + no-go areas in GPX extensions
  (trails:planning namespace) for reimporting into the planner

Also:
- Add no-go area serialization to generateGpx (GPX extensions)
- Parse no-go areas from GPX extensions on import
- Initialize no-go areas in Yjs session from imported GPX
- Save to Journal now exports track only (consistent with Export Route)

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

apps/planner/app/lib/sessions.ts

@@ -90,6 +90,22 @@ export function initializeSessionWithWaypoints(
   });
 }
 
+export function initializeSessionWithNoGoAreas(
+  sessionId: string,
+  noGoAreas: Array<{ points: Array<{ lat: number; lon: number }> }>,
+): void {
+  const doc = getOrCreateDoc(sessionId);
+  const yNoGoAreas = doc.getArray("noGoAreas");
+
+  doc.transact(() => {
+    for (const area of noGoAreas) {
+      const yMap = new Y.Map();
+      yMap.set("points", area.points);
+      yNoGoAreas.push([yMap]);
+    }
+  });
+}
+
 export async function listSessions(): Promise<SessionMetadata[]> {
   return getDb()
     .select()