Sync notes through GPX, Journal, and Planner roundtrip

Full notes lifecycle:
- GPX: description field in GpxData, <metadata><desc> in generate/parse
- Export: Plan GPX and Save to Journal include notes as description
- Journal: updateRoute extracts description from GPX, stores on route
- Reimport: Edit in Planner passes notes via URL params → Yjs Y.Text
- Drop import: GPX with <desc> restores notes in session

Spec updated: session-notes gains GPX export, Journal sync, and
reimport requirements.

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

apps/planner/app/components/PlannerMap.tsx

@@ -614,6 +614,12 @@ export function PlannerMap({ yjs, onRouteRequest, highlightPosition, highlighted
           yMap.set("points", area.points);
           yjs.noGoAreas.push([yMap]);
         }
+
+        // Replace notes if GPX has a description
+        if (gpxData.description) {
+          yjs.notes.delete(0, yjs.notes.length);
+          yjs.notes.insert(0, gpxData.description);
+        }
       }, "local");
     } catch {
       onImportError?.(t("importGpxError"));