/frames/{frame} now validates the frame as a positive 1-based integer and
returns 400 for invalid values. The frame number is threaded through
doWadoRs into addFileToBuffer, where it is sliced out of uncompressed Pixel
Data using NumberOfFrames, Rows, Columns, SamplesPerPixel and BitsAllocated.
- add src/dimse/frameExtractor.ts (native frame slicing)
- add src/dimse/errors.ts (status-bearing HttpError types)
- reject compressed/encapsulated frames with 415 instead of full pixel data
- keep JPEG conversion on /rendered and /thumbnail only
- log frame requests with jpegRendererUsed=false
- add frame extraction and validation tests
