Add mcp logs command for streaming container logs

New server-streaming Logs RPC streams container output to the CLI.
Supports --tail/-n, --follow/-f, --timestamps/-t, --since.

Detects journald log driver and falls back to journalctl (podman logs
can't read journald outside the originating user session). New containers
default to k8s-file via mcp user's containers.conf.

Also adds stream auth interceptor for the agent gRPC server (required
for streaming RPCs).

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

proto/mcp/v1/mcp.proto

@@ -33,6 +33,9 @@ service McpAgentService {
 
   // Node
   rpc NodeStatus(NodeStatusRequest) returns (NodeStatusResponse);
+
+  // Logs
+  rpc Logs(LogsRequest) returns (stream LogsResponse);
 }
 
 // --- Service lifecycle ---
@@ -282,3 +285,18 @@ message PurgeResult {
   // Why eligible, or why refused.
   string reason = 4;
 }
+
+// --- Logs ---
+
+message LogsRequest {
+  string service = 1;
+  string component = 2;    // optional; defaults to first/only component
+  int32 tail = 3;           // number of lines from the end (0 = all)
+  bool follow = 4;          // stream new output
+  bool timestamps = 5;      // prepend timestamps
+  string since = 6;         // show logs since (e.g., "2h", "2026-03-28T00:00:00Z")
+}
+
+message LogsResponse {
+  bytes data = 1;
+}