Remove the unreachable ESRGAN upscale chain

The min-resolution floor lifted small inputs toward SDXL's ~1024 training size,
and Real-ESRGAN was an optional way to do that lifting. Both surviving profiles
run at native geometry, so the engine forced the floor to 0 on every path; the
floor never fired, `upscaling` was never true, and nothing downstream of it could
execute. Gone: upscaler.py, _esrgan_upscale, the min_resolution and upscaler
parameters, _target_size's floor branch, --min-resolution, --upscaler,
_warn_if_esrgan_unavailable and the `esrgan` extra. max_resolution stays and is
now the only lever on geometry; it can only scale down.

scripts/smoke_matrix.py was the one live consumer and neither gate saw it -
Pyright is scoped to src/ and Ruff cannot resolve its function-local import - so
`--diffusion` would have died at import. Its knob rows were written for the
removed profiles besides (--pipeline sdxl, --steps 20, --guidance-scale 5.0,
--device mps), so they are rewritten rather than patched: most now assert a knob
is REJECTED, which is the coverage worth having when the CLI accepts a value the
library refuses several layers down. Accepted-knob rows skip without CUDA, so the
row count is host-dependent and verification-plan.md no longer claims a fixed 68.

This removes a public module, a CLI option and a published extra, so the next
release is 0.25.0, not a patch.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/verification-plan.md

@@ -72,8 +72,10 @@ Run detection, removal, and re-detection over a representative local set. Confir
 
 ### A5. Contract sweep across every parameter choice
 
-`scripts/smoke_matrix.py` (exists, 68 rows, 0 skipped with `--diffusion`) covers every
-choice-valued flag on fixtures. Extend from fixtures to a stratified corpus slice
+`scripts/smoke_matrix.py` covers every choice-valued flag on fixtures. Its knob rows
+were rewritten when the CPU/MPS profiles and the ESRGAN chain were removed: most now
+assert a knob is REJECTED, and the accepted-knob rows skip without a CUDA device, so
+the row count is host-dependent rather than the fixed 68 recorded here before. Extend from fixtures to a stratified corpus slice
 (~500 images spanning format x provenance x aspect ratio), asserting exit-code semantics
 rather than just absence of crash.
 
@@ -85,7 +87,7 @@ sweep asserts on stderr, or the codes get split -- the latter is the better fix.
 
 Compare the flags and values exercised by the matrix against the options declared by
 the CLI. Include optional backends, batch modes, tiling, region-targeted composition,
-the ESRGAN upscaler, and the ffmpeg audio/video strip. The gap to find is not only
+and the ffmpeg audio/video strip. The gap to find is not only
 "logic untested" but
 "never executed on real data", which is precisely what this campaign is for.