P0.2: Proto definitions and code generation

Full gRPC service definition with 12 RPCs: Deploy, StopService,
StartService, RestartService, SyncDesiredState, ListServices,
GetServiceStatus, LiveCheck, AdoptContainers, PushFile, PullFile,
NodeStatus. buf lint passes. Generated Go code compiles.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

buf.yaml

@@ -0,0 +1,9 @@
+version: v2
+modules:
+  - path: proto
+lint:
+  use:
+    - STANDARD
+breaking:
+  use:
+    - FILE