feat: bootstrap secure cross-platform assistant

Establish the Electron foundation and pluggable agent runtime so desktop workflows can evolve safely across supported platforms.

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

src/main/agent/runtime.ts

@@ -0,0 +1,14 @@
+import type {
+  AgentEvent,
+  AgentRequest,
+  AgentRuntimeStatus
+} from '../../shared/contracts'
+
+export interface AgentRuntime {
+  getStatus(): Promise<AgentRuntimeStatus>
+  run(
+    request: AgentRequest,
+    signal: AbortSignal
+  ): AsyncGenerator<AgentEvent, void, void>
+  dispose(): Promise<void>
+}