Phase 1: IPC-Verbindungsschicht + Build-first-Strategie (ADR-0008)

- ADR-0008: Build-first, gesammelte Windows-Validierung (Auftraggeber-Freigabe)
- ADR-0004 vorläufig: Rust auf GStreamer-D3D11-Elementpfad
- ADR-0005 vorläufig: Nuitka Onefolder
- hms_protocol: IpcServer/IpcClient mit Handshake (hello/welcome),
  Capabilities-Austausch, Heartbeat 500 ms bidirektional, Snapshot/Delta,
  Loopback-only-Enforcement, Re-Sync nach Reconnect, Version-Mismatch-Fehler
- 9 Integrationstests: echter TCP-Loopback, kein Mock

schemas/ipc/envelope_v1.schema.json

@@ -8,7 +8,7 @@
   "properties": {
     "protocol_version": {"const": 1},
     "message_id": {"type": "string", "format": "uuid"},
-    "type": {"enum": ["command", "event", "snapshot", "ack", "error", "telemetry"]},
+    "type": {"enum": ["command", "event", "snapshot", "ack", "error", "telemetry", "heartbeat"]},
     "revision": {"type": "integer", "minimum": 0},
     "monotonic_timestamp_ns": {"type": "integer", "minimum": 0},
     "payload": {"type": "object"},