Restore FlagColor model/API/tests here after the parent structured-notes PR dropped them, so this PR remains the coherent home for the FlagColor column and palette.
Remove FlagColor model/API/tests from this PR so schema and EF model stay aligned with the structured-fields migration. FlagColor remains in the follow-on PR that adds its migration.
Persist primary/extra services, service notes, free-text POC, and
tech/vendor notes on create/patch/board/detail instead of embedding
them in description.