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/contracts/channels.ts

@@ -29,6 +29,7 @@ export const ipcChannels = {
   resolveSessionUserInput: 'sessions:resolve-user-input',
   setSessionInteractionMode: 'sessions:set-interaction-mode',
   dismissSessionPlanReview: 'sessions:dismiss-plan-review',
+  dismissSessionMcpAuth: 'sessions:dismiss-mcp-auth',
   querySessions: 'sessions:query',
   updateSessionModelConfig: 'sessions:update-model-config',
   selectProject: 'selection:project',