feat: add secure multi-runtime controls

Make agent backends configurable and governable with encrypted credentials, explicit context sharing, and tool approval boundaries.

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

src/main/agent/runtime.ts

@@ -5,10 +5,12 @@ import type {
 } from '../../shared/contracts'
 
 export interface AgentRuntime {
+  readonly requiresToolApproval: boolean
   getStatus(): Promise<AgentRuntimeStatus>
   run(
     request: AgentRequest,
-    signal: AbortSignal
+    signal: AbortSignal,
+    authorize?: (requiresToolApproval: boolean) => Promise<void>
   ): AsyncGenerator<AgentEvent, void, void>
   dispose(): Promise<void>
 }