feat(0144a): tool registry framework para device-mesh

Anade pkg/tools/devicemesh con Client HTTP al device_agent + ToolRegistry
con 16 tools standard (exec, fs.*, git.*, docker.*, proc.*, pkg.*, shell.eval).
RegisterBuiltins filtra por mode user/sudo via RequiresApproval flag.
Hook al pkg/decision con ActionKindDeviceMesh + DeviceMeshAction.
Runner soporta dispatch via NewRunnerWithDeviceMesh (back-compat NewRunner).

Tests: 25 nuevos en devicemesh + 4 en runner. Build clean.

pkg/decision/devicemesh.go

@@ -0,0 +1,24 @@
+// devicemesh.go: pure data type for "call a device mesh tool" actions.
+//
+// The runtime decides which agent has which tool registry (user vs sudo).
+// The decision layer only describes *what* to call; the runner in
+// shell/effects/ resolves the registry and dispatches.
+package decision
+
+// DeviceMeshAction describes an invocation of a registered devicemesh tool.
+// It is a pure value — no client, no registry, just the name + input.
+//
+// Fields:
+//
+//   - Tool: the registered tool name in the agent's devicemesh.ToolRegistry
+//     (ex "exec", "fs.read", "fs.write").
+//   - Input: LLM-supplied arguments. Will be validated by the registry
+//     before reaching the network.
+//   - ResultKey: optional. The runtime stores the tool result under this key
+//     in the conversation state so the LLM can refer to it later. Empty
+//     string means "do not store, just send back as a tool message".
+type DeviceMeshAction struct {
+	Tool      string
+	Input     map[string]any
+	ResultKey string
+}