feat: add plan mode frontend support with mode toggle and plan review UI

- Add InteractionMode type and ExitPlanModeRequestedEvent to sidecar contracts
- Add PendingPlanReviewRecord domain type and interactionMode to SessionRecord
- Wire onExitPlanMode callback through SidecarClient and RunTurnPendingCommand
- Pass session interaction mode to RunTurnCommand for sidecar consumption
- Handle exit-plan-mode-requested events in AryxAppService
- Add setSessionInteractionMode and dismissSessionPlanReview IPC methods
- Create PlanReviewBanner component with summary, markdown content, and actions
- Add plan mode toggle pill in ChatPane composer area
- Wire implement action as follow-up message (graceful degradation)
- Clear pending plan review on new turn, turn completion, and cancellation

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/main/runTurnPending.test.ts

@@ -17,6 +17,7 @@ describe('run turn pending helpers', () => {
       onActivity: () => undefined,
       onApproval: () => undefined,
       onUserInput: () => undefined,
+      onExitPlanMode: () => undefined,
       errored: false,
     };
 
@@ -40,6 +41,7 @@ describe('run turn pending helpers', () => {
       onActivity: () => undefined,
       onApproval: () => undefined,
       onUserInput: () => undefined,
+      onExitPlanMode: () => undefined,
       errored: false,
     };