[1.0] Make unsupported tracing settings explicitly read-only

The tracing settings UI shows fixed values and confirms saving without a persistence request, which gives operators a false success signal.

Scope

• Render unsupported settings as read-only and explain the effective configuration source.
• Remove the simulated save success and any control that implies persistence not provided by the backend.
• Keep existing trace navigation and accessible labeling/focus behavior.

Acceptance criteria

• The UI cannot report a successful configuration write without a confirmed backend operation.
• Read-only state and any unknown/effective-value limitation are visible.
• A focused UI check covers keyboard interaction and the absence of false save confirmation.

Boundaries

Implementing a new settings persistence API is outside this fix.

References

• Parent topic: #374.
• src/flock/frontend/src/components/settings/TracingSettings.tsx

Start with src/flock/frontend/src/components/settings/TracingSettings.tsx and inspect how fixed tracing values, controls, and save feedback are rendered. Check the existing trace navigation and accessible labeling/focus behavior, then add a focused UI check for keyboard interaction and the absence of false save confirmation. Done means unsupported settings are visibly read-only and no unconfirmed configuration write is reported as successful.