UI: integrate StatusService and configuration pages

Parent: #5451
API dependency: #5477

Summary

Make Status and Configuration the first complete v3alpha-backed Mantine screens by replacing the handwritten API v2 status datasource with generated status.v3alpha.StatusService.GetStatus calls.

Scope

• Consume generated StatusService bindings through the Connect data layer.
• Render version and build information.
• Render cluster name, state, and peers for disabled, settling, ready, and unspecified states.
• Derive uptime from start_time and update its display without refetching the immutable start timestamp unnecessarily.
• Render the original loaded configuration with current Mantine 9 syntax highlighting, copy support, and responsive overflow.
• Handle empty peers, clustering disabled, configuration not yet loaded, Connect errors, cancellation, loading, and retry behavior without assuming optional fields are present.
• Use semantic headings and tables/cards suitable for screen readers and narrow viewports.
• While these are the only complete v3alpha-backed screens, redirect /ui/ to /ui/status; switch the default to Alerts only after the Alerts child lands.
• Remove the handwritten Status type and API v2 query. Remove the generic API v2 fetch layer as soon as no Mantine page uses it.

Acceptance criteria

• Status and Configuration use only generated v3alpha types and StatusService calls.
• No /api/v2/status request or arbitrary JSON cast remains.
• Disabled, settling, ready, unspecified, empty-peer, unavailable, and error states render correctly.
• Uptime is derived from the protobuf timestamp and updates correctly.
• Configuration highlighting/copying is accessible and usable on narrow screens.
• /ui/ redirects to /ui/status until the Alerts page is complete.
• Component tests cover all response and error states with a generated mock transport.
• A real Alertmanager smoke test exercises GetStatus at root and non-root route prefixes.

Dependencies and related work

• Generated Connect client/data layer: #5487.
• Application shell and shared states: #5488.
• StatusService #5477 is complete.
• Track relevant transport-policy changes from #5478.

Likely code areas

• ui/mantine-ui/src/pages/{Status,Config}.page.tsx
• generated status query adapters and tests
• ui/mantine-ui/src/data/status.ts, src/data/api.ts
• route defaults in the application shell