fix: location channel manager

[callebtc]

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[chatgpt-codex-connector]

Repeated beginLiveRefresh piles up location listeners

The new real-time refresh registers continuous updates every time beginLiveRefresh is called, but unlike the previous timer-based implementation it never removes an existing listener before calling requestLocationUpdates. In LocationChannelsSheet the LaunchedEffect keyed on availableChannels and bookmarks re-invokes beginLiveRefresh on each channel update while the sheet stays open, so every location result triggers another registration to the same continuousLocationListener. This stacks multiple active listeners, causing duplicate callbacks and unnecessary background location polling (battery and compute overhead) until the sheet is dismissed.

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