feat: add MCP OAuth authentication frontend wiring and banner

- Add McpOauthRequiredEvent and McpOauthStaticClientConfigEvent to sidecar contracts
- Add PendingMcpAuthRecord domain type with status tracking (pending/authenticating/failed/done)
- Add pendingMcpAuth field to SessionRecord for session-level auth state
- Wire onMcpOAuthRequired callback through sidecarProcess, runTurnPending, and AryxAppService
- Handle mcp-oauth-required events: set session pendingMcpAuth, clear on turn finalize/cancel
- Add dismissSessionMcpAuth IPC channel with preload binding and handler registration
- Create McpAuthBanner component (amber-themed, shows server name/URL, dismiss button)
- Integrate McpAuthBanner into ChatPane with placeholder text and App.tsx callback
- Update test fixtures for new RunTurnPendingCommand.onMcpOAuthRequired field

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

src/shared/domain/mcpAuth.ts

@@ -0,0 +1,19 @@
+export type McpAuthStatus = 'pending' | 'authenticating' | 'authenticated' | 'failed';
+
+export interface McpOauthStaticClientConfig {
+  clientId: string;
+  publicClient?: boolean;
+}
+
+export interface PendingMcpAuthRecord {
+  id: string;
+  status: McpAuthStatus;
+  agentId?: string;
+  agentName?: string;
+  serverName: string;
+  serverUrl: string;
+  staticClientConfig?: McpOauthStaticClientConfig;
+  requestedAt: string;
+  completedAt?: string;
+  errorMessage?: string;
+}

src/shared/domain/session.ts

@@ -13,6 +13,7 @@ import {
 import type { SessionRunRecord } from '@shared/domain/runTimeline';
 import type { PendingUserInputRecord } from '@shared/domain/userInput';
 import type { PendingPlanReviewRecord } from '@shared/domain/planReview';
+import type { PendingMcpAuthRecord } from '@shared/domain/mcpAuth';
 import type { InteractionMode } from '@shared/contracts/sidecar';
 
 export type ChatRole = 'system' | 'user' | 'assistant';
@@ -54,6 +55,7 @@ export interface SessionRecord {
   pendingApprovalQueue?: PendingApprovalRecord[];
   pendingUserInput?: PendingUserInputRecord;
   pendingPlanReview?: PendingPlanReviewRecord;
+  pendingMcpAuth?: PendingMcpAuthRecord;
   runs: SessionRunRecord[];
 }