Add navigation, Orin runtime and data flow design; rework repo naming

Navigation: self-hosted MapLibre + Valhalla + PMTiles, offline-first, with
Japan specifics (left-hand traffic via valhalla_build_admins, data volume,
CJK labels). Map matching pulled forward as Phase 2 ground truth.

Orin runtime: new document covering the 8 GB shared-memory budget,
capture-first startup tiers, failure isolation, storage and the audio graph.

Data flow: direction belongs to topics inside the Orin; the display boundary
is two simplex channels rather than one duplex socket; cloud links are
outbound-initiated only; services mock themselves rather than having separate
stub implementations.

Naming: repositories are <group>-<thing> with no project prefix, so lexical
order matches semantic grouping. Indexes the five new repos.

Decisions 8-19 recorded; 14 (recording retention) left open.

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

README.md

@@ -11,6 +11,7 @@ indexed here.
 
 - [Overview](OVERVIEW.md) — what the system is meant to do
 - [Architecture](docs/ARCHITECTURE.md) — system shape, services, message bus, display contract
+- [Orin runtime](docs/ORIN-RUNTIME.md) — what runs on the board: memory budget, startup tiers, audio
 - [Repositories](docs/REPOS.md) — repo layout, naming, template-repo policy
 - [Roadmap](docs/ROADMAP.md) — phases and current status