feat(train): a recording follows a route, its turns told (ADR 0030, D45)

The Record sheet offers the routes with a way planned; the recorder's
service follows the one chosen offline (RouteGuide.kt): turns told 50 m
before them (100 m on a bike) after a tone, off the route past 40 m for
10 s a cue with the way back, told again on rejoining, the end told.
The recording file keeps the route and the guidance; the recording
screen shows the next turn or the way back, and swipes to a map of the
route, the track and the position, north or the heading up.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

docs/adr/0030-halkyon-train.md

@@ -898,6 +898,31 @@ Strava. What was found, 27 Oct:
   (to CoMaps or anything, with waypoints and turn hints) and come in as GPX shared to
   Train or opened in it, snapped to a profile or kept as drawn (over out alone, and
   over neither yet).
+  Built: following in a recording (9c). The Record sheet offers the routes with a
+  way planned, for an activity with GPS, and a route for an activity chooses it, as a
+  plan does. The app hands the service the route's points, its turns each with its
+  line in the app's language ("In 50 metres: Turn left"; BRouter's beelines and
+  off-route marks aren't turns, and are left out), and the words off the route with
+  places for the figures, through a file beside the app's (`route.json`), since an
+  intent carries less than a route's thousands of points. `RouteGuide.kt` places each
+  fix precise enough on the route (among its next 500 m and last 100 m first, the
+  whole route where none is near, so that a shortcut or a figure eight finds its
+  place), none while paused; a turn is told once, 50 m (100 m on a bike) along the
+  route before it, a tone first and the line 0.4 s after; one passed unseen is
+  skipped. Off the route: past 40 m for 10 s, a double vibration and the way back
+  ("It lies 80 metres to the north-east", to 10 m, to the nearest point), again
+  every minute while still off (a runner off for long would otherwise hear it once),
+  told again once back within 30 m (so that a fix wavering about 40 m doesn't cue
+  over and over); no turn is told while off. The end is told once within 30 m of it.
+  The file keeps the route (`route`, its payload) and what following it gave
+  (`guide … next|turn|off|on|arrived`), so a recording the app comes back to shows it
+  again. The recording screen shows the next turn with how far it is as the crow
+  flies (the service places the person, the app only reads its lines), or the way
+  back; it swipes to a map of the route, the track so far (the fixes precise enough
+  to count) and the position, which the map follows, zoomed with two fingers alone
+  so that a swipe goes back to the figures, north up by default and the heading up
+  (of the last 5 m or more) as tapped. A saved workout doesn't keep which route it
+  followed yet.
 - **D46 Train's server on the instance** (recommended, the developer's; 28 Oct): it
   joins learn.halkyon.eu's server, as BRouter needs a server of Train's to ask it
   (D11, D22), at **train.halkyon.eu** (over a path on learn.halkyon.eu, which would