test(wpf): capture fractional local ShaderEffect frames

[wieslawsoltes]

Scope

Stacked reference-only companion to #276. Native implementation is separately stacked on #277; this PR changes no native admission, renderer, source dependency pin or WPF551 code.

• Add 21 actual original Microsoft WPF ShaderEffect cases, 63 cold/warm/independent replays and 23 separately rendered ordinary-drawing baselines.
• Preserve Rect(16.75,16.25,15.5,7.5), original padding doubles, DPI1/2, complete scale-space capture allocation, final clipping, implicit input, constant/UV/derivative/ImageBrush output, and same-effect padding/reset ownership.
• Exercise noncommuting nested float transforms and separately narrowed matrix history; retain deferred fractional-final constant and UV-squared source controls without admitting them natively.
• Require full exact pixels, visible independent white/colored baselines and opaque alpha. SOFTWARE integer-origin UV and hardware pixel-center UV remain explicitly distinct.
• Preserve all original 25 arithmetic shaders, 28 sampler cases/84 replays/19 controls, 13 padding cases/39 replays/38 controls and every deadline. All new artifacts use CreateNew; a failure preserves the full new inventory and qualifies zero new cases. ARM64 remains the original explicit unavailable-software negative lane.

Validation

Implementation was committed before checks. Bounded CPU-only validation passes 127 pure controls (57 unchanged +70 new), direct compilation of only the original reference sources against cached Microsoft reference assemblies with warnings as errors, syntax parsing, workflow YAML, unchanged original guards/deadlines and diff checks.

No original Windows execution, native/provider build, local GPU/VM, runtime staging or hardware/application qualification is claimed. The automatic original-Windows reference workflow is the next gate. Full native Build is deliberately deferred while this draft remains stacked; no merge without eventual exact-head whole-Build and all required checks.

Source contract and precise receipt: docs/original-shader-local-capture-reference.md.

[wieslawsoltes]

The exact corrected head e611aae passed original Windows reference workflow https://github.com/wieslawsoltes/ProGPU/actions/runs/37045784511 (both jobs successful). The x64 lane checked all 21 new cases/63 replays against the source-derived output clip; ARM64 passed only its separate unsupported-software negative controls. Capture allocation, UV basis, source inputs and strict byte comparisons remain unchanged. Offline reanalysis also matched all 1,548,288 immutable predecessor bytes. This is original-reference evidence, not native GPU/application qualification; full Build and stacked dependencies remain pending.