Verify Valhalla on arm64; correct driving-side and retention decisions

arm64 is no longer a risk: verified end to end on mikkeli-orin-nano-2
(L4T R36.4.7). The official image publishes linux/arm64, runs natively, and
the full pipeline works including a served route.

Corrects the Japan guidance. Advising a regional extract was wrong for the
admin build: driving side is a country-level property, and a Shikoku extract
produces no country row and drive_on_right=1, silently giving right-hand
traffic routing. Admins must come from the full extract; routing tiles may
still come from a region.

Decision 14 closed: recordings bounded with rotation, enforced by the writer.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013kj58Jugkic783b8ZrtTVZ

docs/ROADMAP.md

@@ -66,10 +66,10 @@ Not a phase — it runs alongside, and its early output feeds Phase 2. Design is
 in [ARCHITECTURE.md](ARCHITECTURE.md#navigation); code in `svc-nav` (runtime)
 and `tool-mapmint` (artifact builds).
 
-- [ ] Confirm Valhalla builds and runs on the Jetson (arm64) — do this first,
-      it is the one real integration risk
-- [ ] Build the admin database with `valhalla_build_admins` — this is what sets
-      left-hand traffic, and it must run before the tile build
+- [x] Confirm Valhalla builds and runs on the Jetson (arm64) — done 2026-09-04,
+      full pipeline verified on the Orin including a served route
+- [ ] Build the admin database with `valhalla_build_admins` **from the full Japan
+      extract** — a sub-region silently yields right-hand-traffic routing
 - [ ] Build Valhalla routing tiles from a Geofabrik Japan extract, starting with
       the region actually driven rather than all 2.3 GB of it
 - [ ] Pull a Japan basemap extract from the Protomaps daily build with