Break up route-features into focused specs, add new changes

Archive the monolithic route-features spec and replace with 9 focused
OpenSpec changes: multi-day-routes, waypoint-notes (with POI snapping),
undo-redo, local-dev-stack, route-sharing, route-discovery,
activity-photos, osm-overlays, plus the existing changelog and
komoot-import.

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

openspec/changes/route-discovery/proposal.md

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+## Why
+
+The Journal currently has no way to discover routes other users have published.
+Each user's route list is isolated -- you can only see your own routes. Once
+route-sharing adds public visibility, there needs to be a way to actually find
+those public routes. Without discovery, making a route public has no effect.
+
+Outdoor platforms live and die by discovery. A hiker planning a trip to the
+Harz Mountains should be able to pan the map there and see what routes exist.
+This is the most natural interface for spatial data: a map.
+
+## What Changes
+
+- **Explore page**: A new `/routes/explore` page in the Journal with a full-page
+  Leaflet map. Users pan and zoom to browse public routes in any area.
+- **Bounding box API**: A server endpoint that takes the current map viewport
+  bounds and returns public routes whose geometry intersects the bounding box,
+  using PostGIS `ST_Intersects`. Results are limited to 50 and geometries are
+  simplified for transfer performance.
+- **Route polylines**: Public routes rendered as clickable polylines on the
+  explore map. Clicking a route shows a popup with name, distance, elevation
+  gain, author, and a link to the route detail page.
+- **Spatial index**: Verify (or create) a GiST index on `journal.routes.geom`
+  to keep bounding box queries fast.
+
+## Capabilities
+
+### New Capabilities
+
+- `route-discovery`: Map-based exploration of public routes via spatial queries
+
+### Modified Capabilities
+
+- `journal-navigation`: Add explore link to main navigation
+- `map-display`: Route polylines with interactive popups on explore map
+
+## Non-Goals
+
+- **Full-text search**: No searching routes by name or description. Map browsing
+  is the only discovery mechanism for now.
+- **Filtering**: No filtering by distance, elevation, activity type, difficulty,
+  or tags. These are useful but add complexity -- defer until real users ask.
+- **Recommendations**: No "routes you might like" or personalized suggestions.
+- **Clustering**: No marker clustering for dense areas. The 50-result limit and
+  geometry simplification keep the map readable. Clustering can come later.
+- **Federated discovery**: Routes from other Journal instances are out of scope.
+  This only covers routes on the local instance.
+
+## Dependencies
+
+- **route-sharing** (route-features change, section 1): The `visibility` column
+  on `journal.routes` must exist before this change can query for public routes.
+  Without it, there are no public routes to discover.
+
+## Impact
+
+- **Database**: GiST spatial index on `journal.routes.geom` (may already exist)
+- **New route**: `/routes/explore` page + API endpoint
+- **Navigation**: Explore link added to Journal nav
+- **Packages**: Uses `@trails-cool/map` (MapView, RouteLayer) -- may need a new
+  component for interactive route polylines with popups
+- **i18n**: New keys for explore page UI (en + de)