Adopt shared export-name converter for Layer Metadata table

[razbroc]

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

• Shared canonical export-name converter (camelCase to snake_case with override table) raster-shared#211