WatermarkResponseModel gains ImageSource so a client can identify
logo-driven presets generically instead of matching a user-editable name.
Additive under the frozen-additive /api/v1 contract (#286).
Adding a positional record parameter is source-breaking for existing
constructor call sites, so the two test files that built the DTO
positionally are updated. WatermarkHandlerTests now seeds its two rows with
DIFFERENT image sources so the round-trip assertion proves the field is
actually carried through the mapper rather than matching a constant on both.
Regenerated v1.json, endpoint-index.md and v1.d.ts; check:api clean.
Stripped the inherited UTF-8 BOM from Mapper.cs (#311 fix-as-you-touch).
Refs #67
timothy
ebaadc0656