test(calibration): self-contained end-to-end regression test

The committed calibration service (model.py/calibrate.py/infer.py) had no
automated test — only ad-hoc verification. Adds a CPU-only, no-real-checkpoint
test that exercises the CLI end-to-end on synthetic data: build base ->
calibrate.py fits adapter -> infer.py runs base+adapter, asserting adapter
size (<200KB), keypoint shape [N,17,2], finiteness, [0,1] range, and that the
adapter actually changes the output. Passes on Windows CPU (torch 2.11).

Co-Authored-By: claude-flow <ruv@ruv.net>