build(train): Train's server and BRouter deployable beside the instance (ADR 0030, D46)

deploy/compose.train.yaml adds Train's server at train.halkyon.eu, a
member of Learn's register, with its database halkyon_train in the
instance's PostgreSQL, and BRouter beside it alone (v1.7.10, checked by
SHA-256, no log), its segments of the operator's region kept current
monthly. Nothing changes until deploy/.env names the compose file:
redeploy.sh and backup.sh take Train in only then, and the operator's
steps are in sidecars/README.md. restic now forgets snapshots grouped by
host alone, so adding Train's dump leaves no group behind for good.

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

@@ -1,6 +1,6 @@
 # ADR 0030: Halkyon Train, what it does and where its data comes from
 
-- **Status:** decided 27–28 Oct 2026, by the developer (D1–D45 below). The shell (D12)
+- **Status:** decided 27–28 Oct 2026, by the developer (D1–D46 below). The shell (D12)
   is built; recording (D13–D28) is built on Android, iOS waiting for a Mac; Health
   Connect (D29–D31) is built; the Loop's setup and keeping (7a, D34–D36) and its
   daily data (7b, D37, D38), its sessions (7c, D39) and its firmware (D10, D40) are
@@ -881,6 +881,28 @@ 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).
+- **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
+  carry Learn's name for good); its data in the instance's PostgreSQL as a database of
+  its own, `halkyon_train`, under a role that can't connect to Learn's (over a second
+  PostgreSQL, twice the memory and a second backup); a **member of the instance's
+  register** on Learn's server (ADR 0016: one account a person across the operator's
+  services, over a register of its own). It is a compose file of its own,
+  `deploy/compose.train.yaml`, switched on in `.env` as the sidecars are, so nothing
+  changes on the instance until the operator does (the steps in
+  `deploy/sidecars/README.md`, *Train*); `redeploy.sh` then builds, dumps, migrates
+  and waits for it as for Learn's server, and `backup.sh` backs its database up in the
+  same snapshots. BRouter (v1.7.10, its release checked by SHA-256) runs beside Train's
+  server alone, on a network without a way out, with no log (it writes the waypoints),
+  its segments refreshed monthly by a container of its own; Europe's took 3.3 GB on
+  28 Oct. Whether the server's disk has room is the developer's to check before
+  switching it on. The map stays OpenFreeMap's: the PMTiles sidecar needs a style for
+  Protomaps' schema, a step of its own (about 40 GB for Europe, estimated from the
+  planet's 120 GB). Learn's server signs in to PostgreSQL as its superuser, so it could
+  read Train's database; a role of its own for it is left for later. restic now forgets
+  snapshots grouped by host alone, so that the snapshots before Train's dump joined
+  them aren't kept for good as a group of their own.
 
 ## Consequences