Adopt shared export-name converter for Layer Metadata table

Nobody has claimed this yet.

## What to build

Replace Overseer's private `convertObjectKeysToSnakeCase` with the shared canonical export-name converter from `raster-shared`, so the **Layer Metadata** export table and the **Layer Parts** export table derive their column names from one source.

This is behavior-preserving for Overseer's current output: the Layer Metadata feature has no plain `resolutionDegree` key (it uses the already-abbreviated `maxResolutionDeg`/`minResolutionDeg`), so the new override does not change Overseer's columns. Bump Overseer's `raster-shared` dependency to the version from the blocking issue and remove the duplicated local converter.

## Acceptance criteria

- [ ] Overseer imports and uses the shared export-name converter from `raster-shared`.
- [ ] Overseer's private `convertObjectKeysToSnakeCase` is removed.
- [ ] The Layer Metadata table's column names are unchanged from current behavior (verified by existing/added tests).
- [ ] Overseer depends on the `raster-shared` version delivered in the blocking issue.

## Blocked by

- MapColonies/raster-shared#211

Locate Overseer's private convertObjectKeysToSnakeCase and the Layer Metadata and Layer Parts export-table code, then inspect the current raster-shared dependency version. Read the blocking raster-shared#211 issue before changing the dependency. Done means both tables use the shared converter, the private copy is gone, and tests confirm Layer Metadata column names are unchanged.

Written by the indexing model from the issue text.