Add live countdown for GPS skip in auto-ping mode

[Copilot]

When auto-ping skips due to stale GPS (after refresh timeout), the status previously showed a static message then reverted to generic text without countdown, obscuring that auto-ping remained active.

Changes

• Track skip state: Added skipReason to state, set to "gps too old" when GPS refresh fails
• Conditional countdown display: Show "Skipped (gps too old), next ping (Xs)" with live countdown and warning color when skip occurs; normal countdown otherwise
• Enhanced countdown timer: Support object return format {message, color} alongside existing string format
• Lifecycle management: Clear skipReason on auto-ping start/stop and before next attempt

Implementation

// Countdown message generator now returns color-coded objects
if (state.skipReason) {
  return { 
    message: `Skipped (${state.skipReason}), next ping (${remainingSec}s)`,
    color: STATUS_COLORS.warning  // Amber background
  };
}
return { 
  message: `Waiting for next auto ping (${remainingSec}s)`,
  color: STATUS_COLORS.idle  // Gray background
};

GPS refresh failure path:

try {
  return await acquireFreshGpsPosition();
} catch (e) {
  state.skipReason = "gps too old";  // Triggers skip countdown
  return null;
}

Screenshots

Normal countdown (gray):

GPS skip countdown (amber):

Original prompt

In the previous PR (“Add GPS status feedback and freshness validation for ping operations”) auto‑ping behavior is mostly correct, but there’s a minor status/UX issue when GPS data is stale.

Problem

• In auto ping mode, if GPS data is too old, the UI correctly shows:
  "GPS data old, trying to refresh position"
• However, after the refresh attempt times out, the status reverts to:
  "waiting for next ping"
• This makes it look like the ping succeeded (or wasn’t skipped), when in fact it was skipped due to stale GPS.

Requested change

• When an auto ping is skipped because GPS is too old (including after a refresh attempt times out), the status should explicitly indicate the skip and then show the next scheduled attempt with a countdown.

Desired status text (exact wording)

• "Ping skipped, gps too old. waiting for next ping (30s)"

Countdown behavior

• The "30s" value should be a live countdown to the next auto‑ping interval (decrementing each second until the next attempt).
• This ensures the user understands:
  1. the ping did not occur (it was skipped/failed due to stale GPS), and
  2. auto‑ping is still running and will try again at the next interval.

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