feat(runtime): add integration hardening and diagnostics

README.md

@@ -63,6 +63,12 @@ $HOME/.platformio/penv/bin/pio device monitor
 A successful boot reports the firmware version, LittleFS capacity and use,
 network state, HTTP service startup, and health state `serving`.
 
+The production integration/load procedure and its fixed resource thresholds
+are documented in `docs/INTEGRATION_TESTING.md` and
+`docs/RESOURCE_BUDGET.md`. Runtime counters and internal-memory samples are
+available from `GET /diagnostics`; the endpoint contains no credentials,
+session tokens, or game projection.
+
 ## Wi-Fi provisioning and recovery
 
 With no saved credentials, or after a failed station connection, the device