Fix zombie detection stopping logging after GPS denial

[tvancott42]

Summary

• Zombie detection was incorrectly stopping all signal logging when GPS permission was denied. The GPS watcher fires a single error callback on denial then goes silent - the same silence pattern as a dead browser. Now skips the zombie check when _gpsDenied is true so signal data keeps logging without coordinates.
• UI indicator ("Live · Logging") now correctly switches to "Live" when zombie detection stops persistence, instead of continuing to show "Logging" while silently discarding data.

Test plan

• GPS allowed + close: zombie kills in ~15s, no stale GPS repeating
• GPS denied + keep running: logs signal data without coords indefinitely
• GPS denied + close: circuit timeout kills in ~3 min (benign null-GPS data)
• GPS revoked mid-session: zombie kills in ~15s
• GPS blocked (pre-set): denied banner shows, keeps logging
• Full matrix tested across iOS Firefox and Safari (18 test cases)