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>

packages/gpx/src/generate.ts

@@ -4,15 +4,23 @@ import type { TrackPoint } from "./types.ts";
 /**
  * Generate a GPX XML string from waypoints and track points.
  */
+export interface NoGoArea {
+  points: Array<{ lat: number; lon: number }>;
+}
+
 export function generateGpx(options: {
   name?: string;
   waypoints?: Waypoint[];
   tracks?: TrackPoint[][];
+  noGoAreas?: NoGoArea[];
 }): string {
+  const hasExtensions = options.noGoAreas && options.noGoAreas.length > 0;
   const lines: string[] = [
     '<?xml version="1.0" encoding="UTF-8"?>',
     '<gpx version="1.1" creator="trails.cool"',
-    '  xmlns="http://www.topografix.com/GPX/1/1">',
+    '  xmlns="http://www.topografix.com/GPX/1/1"' +
+      (hasExtensions ? '\n  xmlns:trails="https://trails.cool/gpx/1"' : "") +
+      ">",
   ];
 
   if (options.name) {
@@ -46,6 +54,18 @@ export function generateGpx(options: {
     }
   }
 
+  if (options.noGoAreas && options.noGoAreas.length > 0) {
+    lines.push("  <extensions>", "    <trails:planning>");
+    for (const area of options.noGoAreas) {
+      lines.push("      <trails:nogo>");
+      for (const pt of area.points) {
+        lines.push(`        <trails:point lat="${pt.lat}" lon="${pt.lon}"/>`);
+      }
+      lines.push("      </trails:nogo>");
+    }
+    lines.push("    </trails:planning>", "  </extensions>");
+  }
+
   lines.push("</gpx>");
   return lines.join("\n");
 }