GeoTIFF map overlays disappear when switching vehicles

## Problem

GeoTIFF overlays vanish when the user connects to a different vehicle, even with the same user. Reported by a user who imported overlays, switched vehicles, and found a different (empty) overlay list.

The raster bytes are still on disk — only the record of them is gone — so the data is invisible and unreclaimable through the UI.

## Cause

The two halves of an overlay are stored with different scopes:

- **Raster bytes**: localforage IndexedDB instance `Cockpit - Map Overlays` / `cockpit-map-overlays-db` (`src/libs/map/overlay-storage.ts:13-18`), keyed by a uuid. Origin-global, machine-local.
- **Metadata (including that uuid)**: a settings key (`src/stores/mission.ts:130`):

```ts
const mapOverlays = useBlueOsStorage('cockpit-map-overlays-v1', [])
```

`useBlueOsStorage` stores under `cockpit-settings-v2[user][vehicle]` and syncs to BlueOS under `settings/{userId}/`. So the only pointer to a machine-local blob is scoped per user × vehicle.

A first-time vehicle usually looks fine, because `runVehicleGettingOnlinePipeline` falls back to the last connected vehicle's package (`src/libs/settings-management.ts:1126-1164`). The breakage appears once both vehicles already have their own settings package: the current combo hits, and overlays imported under vehicle A are simply not in vehicle B's list.

## Consequences

1. **Orphaned rasters.** Overlays imported under one profile are unreachable from another. Their bytes stay in IndexedDB consuming quota, referenced by nothing, with no UI to reclaim them.

2. **Silent dangling references.** Because the key syncs through BlueOS, a second ground station connecting to the same vehicle pulls down metadata whose uuids only exist in the first machine's IndexedDB. The overlay is listed and ticked visible, and never draws — the only signal is a console warning (`src/composables/map/useMapOverlays.ts:150-154`):

```ts
const blob = await mapOverlayStorage.getItem(meta.id)
if (!blob) {
console.warn(`Map overlay "${meta.name}" has no stored raster; skipping render.`)
return
}
```

3. **Cross-profile deletion.** The fallback copy duplicates metadata including the uuids, so two vehicle slices can reference the same raster. Removing the overlay under one calls `deleteStoredOverlay` (`src/components/map/MapOverlaysDialog.vue:213-216`), which deletes the shared bytes globally, leaving the other profile with an entry that can never render.

Start by tracing the overlay metadata in src/stores/mission.ts:130, raster storage in src/libs/map/overlay-storage.ts:13-18, and vehicle settings fallback in src/libs/settings-management.ts:1126-1164. Reproduce switching between vehicles and inspect rendering in src/composables/map/useMapOverlays.ts:150-154 and deletion in src/components/map/MapOverlaysDialog.vue:213-216. Done should prevent overlays from becoming inaccessible or dangling across vehicle profiles.

Written by the indexing model from the issue text.