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>

tests/main/runTurnPending.test.ts

@@ -18,6 +18,7 @@ describe('run turn pending helpers', () => {
       onApproval: () => undefined,
       onUserInput: () => undefined,
       onExitPlanMode: () => undefined,
+      onMcpOAuthRequired: () => undefined,
       errored: false,
     };
 
@@ -42,6 +43,7 @@ describe('run turn pending helpers', () => {
       onApproval: () => undefined,
       onUserInput: () => undefined,
       onExitPlanMode: () => undefined,
+      onMcpOAuthRequired: () => undefined,
       errored: false,
     };