Index contracts; record the envelope's two clocks and single-source rule

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

docs/REPOS.md

@@ -23,6 +23,7 @@ contracts repo, not copied into each consumer.
 | [project-yukart](gitea:yukart/project-yukart) | Hub: overview, roadmap, architecture |
 | [orin-nano-env-setup](gitea:yukart/orin-nano-env-setup) | Jetson host bring-up |
 | [app-flutter](gitea:yukart/app-flutter) | Flutter display client |
+| [contracts](gitea:yukart/contracts) | Topic namespace, payload schemas, signal registry |
 | [svc-gw](gitea:yukart/svc-gw) | Telemetry gateway — aggregation and the HTTP surface |
 | [svc-nav](gitea:yukart/svc-nav) | Navigation service — routing and guidance |
 | [tool-mapmint](gitea:yukart/tool-mapmint) | Map artifact minting, workstation-side |
@@ -32,7 +33,6 @@ contracts repo, not copied into each consumer.
 
 | Repository | Role | Why separate |
 |---|---|---|
-| `contracts` | Topic namespace, payload schemas, Z27AG DBC | Consumed by every other repo, including non-Jetson clients; must not be duplicated |
 | `svc-core` | Acquisition + processing cluster: `can-bridge`, `obd-poller`, `gnss`, `decoder`, `recorder` | Developed and deployed as one unit on the Orin |
 | `app-esp32` | ESP32 RLCD/e-ink display firmware (Class B) | Embedded toolchain, flashed not deployed |
 | `tool-analysis` | Offline session analysis, reverse-engineering notebooks | Runs off-car, no runtime coupling |