feat(journey): draw the trips' GPX tracks on the journey map (#1911)

* feat(journey): serve the GPX tracks behind a journey

A journey has no trip of its own, but every entry records the trip it came from,
and a trip's routed geometries live on its places. So the tracks are derivable
without any new storage: GET /journeys/:id/tracks walks that link and returns the
geometries, dropping elevation nothing on the map reads and skipping anything
that is not a usable line.

* feat(journey): draw those tracks on the journey map

Both renderers, Leaflet and GL, plus the mobile map-timeline that shares them.
Solid and in the track's own colour with a white casing, so it reads as a
recorded route rather than as the dashed line that merely connects entries in
time order, and stays legible on satellite tiles.

* feat(journey): load the tracks alongside the journey

Fetched separately from the journey itself: most journeys have no tracks, and a
failed lookup should cost the map its lines rather than the whole page.

* docs(journey): document the GPX tracks on the map

* fix(journey): label tracks with the house map tooltip

bindTooltip's default box ignores the appearance tokens, so it sat there in
Leaflet grey next to markers already using .map-tooltip. Same class now, and an
unnamed track gets no tooltip at all instead of an empty one.

wiki/Journey-Journal.md

@@ -55,6 +55,10 @@ On mobile, entries are displayed in a horizontal scrolling timeline of card thum
 
 The journey detail page includes a map on the right (desktop) or an integrated map-timeline (mobile) showing all entry locations alongside the places from linked trips.
 
+**GPX tracks are drawn too.** Any route you imported into one of the journey's linked trips, from a `.gpx`, `.kml` or `.kmz` file, appears on the journey map as well, in the same colour it has in the trip planner and with a white casing so it stays readable on satellite tiles. Nothing to switch on: the tracks belong to the trips your entries came from, so importing the file while planning is all it takes. Hovering a track shows its name.
+
+The thin dashed line connecting entries in date order is something else and stays as it is: that one is drawn by TREK, while a track is the route you actually recorded.
+
 ![Journey detail page for "Autumn in Japan" with its cover header and day/place/entry/photo counts, the day-by-day timeline with Add Entry actions on the left, and the entry map on the right](assets/JourneyDetail.png)
 
 ## Plugin entry rows