feat(map): add USFS trails and roads layer

- Add USFS trails/roads as toggleable map layer via PMTiles
- Trails: dashed brown lines, roads: solid khaki lines
- Labels at zoom 12+ for trail and road names
- Click handler shows popup with trail/road info
- Feature-flag gated with has_usfs_trails (default false)
- Add Trails toggle to Layer Control panel

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/config.js

@@ -33,6 +33,7 @@ const FALLBACK_CONFIG = {
     has_contours_test: true,
     has_contours_test_10ft: false,
     has_address_book_write: false,
+    has_usfs_trails: false,
     has_contacts: false,
   },
   defaults: {