Add GET /api/channels, move endpoints under /api prefix, serve Scalar docs at / (issue #1)

- New GET /api/channels: device Meshtastic channels from FromRadio.channel
  frames during initial sync; psk/keys redacted; map reset on reconnect.
- app.setGlobalPrefix('api'): /status -> /api/status, /send -> /api/send.
- Scalar API docs at / (OpenAPI JSON at /docs-json) via @nestjs/swagger +
  @scalar/nestjs-api-reference; light swagger decorators on endpoints/body.
- MESH_RECONNECT_MS env knob (default 5000 ms).
- v0.1.0: CHANGELOG entry, README/AGENTS/ORCHESTRATOR docs sync.

tsconfig.json

@@ -3,6 +3,7 @@
     "module": "nodenext",
     "moduleResolution": "nodenext",
     "resolvePackageJsonExports": true,
+    "resolveJsonModule": true,
     "esModuleInterop": true,
     "isolatedModules": true,
     "declaration": true,