Preserve TUI status timing when the status row is hidden

[copyberry]

Preserve TUI status timing when the status row is hidden

Why

Streaming can temporarily hide the status row, but its elapsed time is still
needed when the row returns and when the final Worked for duration falls back
to the local clock. Approval prompts must also keep that clock paused.

What changed

• Own the pause-aware status timer in the bottom pane independently of the
  optional status row.
• Preserve elapsed time and modal pause state while hiding or restoring the row,
  and reset the clock for new turns and Windows sandbox setup.
• Use the independent timer as the fallback for the final turn duration.

Testing

Add timer unit coverage and TUI tests for hidden rows, outstanding approvals,
fallback turn durations, and fresh Windows sandbox setup clocks.

[github-actions]

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