Count named trail paths as hikes where trails aren't mapped as hiking routes

[jtopgi]

Why

This is the second step of the plan you chose ("buses and ferries …, then hikes from named trail paths"). Searches only used OpenStreetMap hiking-route relations, but across the American West most trails are mapped as named paths, with no relation:

Hills near	Hiking-route relations	Named trails mapped only as paths
NYC: Hudson Highlands	203	309
Seattle: Issaquah Alps	134	437
Portland: Columbia Gorge	30	218
SF: Marin / Mt Tam	55	204
LA: San Gabriels	8	135

How

• Tiles. The tile query now also lists named footpaths, bridleways and paths (OverpassService::PATH_FILTER). It skips sidewalks, crossings, private paths and ways that belong to a hiking route (- .routed).
  • Ways come with their tags, nodes and bounding box, but not their geometry. That's about 3 MB per four tiles around the Issaquah Alps or Marin, taking 17–23 s.
  • Full geometry would have been 3.5–6.5 MB per two tiles, over the 8 MB response limit.
  • LONG_QUERY_SECONDS and the query timeout go from 45/40 to 60.
• Grouping. Ways with the same name that share a node become one trail, using union-find (path_candidates). Each trail is a candidate with the negative of its first way's id, which no relation can have, plus its ways.
  • TILE_KEY is bumped to v3.
  • Named paths are half a point less promising than mapped hiking routes (PATH_PROMISE), so places rich in relations change little.
• Details. TrailsService::Search#known remembers each candidate path's ways, and trails_for / routes / fetch_routes take paths:.
  • The details query fetches the picked paths' ways with geometry (way(id:…)->.named; out tags geom) together with relations. It measures length, loop, a loose-end start, the preview and the paved share (path_attributes), and stores ways in the details.
  • A path requested without its ways is skipped, never cached as unmeasurable.
• Highlights. Highlights are looked up along a named path's ways, read from its stored details (path_ways), so the hike page works too.
• Links. Trail#osm_url points to /way/<first way> for paths. The hike page accepts negative route ids.
• Route database. It needs no change: negative ids import as they are, and details keep their ways.
• Fixes from review:
  • Dense areas. Where named paths push a tile query over 8 MB, as around Zürich, those tiles are queried again for their hiking routes alone. They keep their routes, and a response that large no longer counts as an Overpass outage.
  • Trails at tile edges. Paths are listed 0.05° beyond each tile so short trails crossing an edge arrive whole. Pieces from different tiles, including the first four and the rest, are joined where they share a way, and keep the id of a piece already checked.
  • Re-measuring. A path measured from fewer ways than are now known is measured again. If that fails, as Overpass does from the server, it keeps the stored details and waits 6 hours before retrying. Details record the ways they were measured from, so ways deleted since don't trigger refetches.
• README updated.

Verified locally (live providers, Overpass mirror)

• San Francisco, from Caltrain 4th & King: 30 hikes, 20 of them named paths. They include Montara Mountain, Hazelnut Trail, Redwood Regional's French Trail and Sweeney Ridge. Earlier test builds found 0.
• New York, from Grand Central: 28 hikes, only 1 of them a named path, up from 26 with relations only. Hiking routes still lead where they're mapped, as intended.

Tests

• Path candidates: grouping by shared nodes, the same name elsewhere kept separate, and short paths dropped.
• Measuring a path from its ways, with the paved share, a loose-end start and ways kept.
• Highlights along a path's ways.
• A path without known ways is neither queried nor written off.
• Promise; the route database round trip.
• The hike page for a named path (highlights, and the /way/5 link); a route id of 0 is rejected.
• The search passes paths' ways to trails_for.
• Exact query strings updated.
• Full suite (295), system tests, Brakeman and Zeitwerk pass.