feat: retain original MIL ShaderEffect padding in integral captures

[wieslawsoltes]

Implementation

Retains all four original ShaderEffect padding doubles and atomically validates them before publication. Nonzero padding inflates float local edges before the existing positive-axis transform; the zero-padding path is unchanged. Adds a typed managed overload without changing the existing wire layout or legacy overload bytes.

Expanded bounds use the existing isolated capture, complete sampler frame, derivatives, final clipping and source ownership. Fractional physical frames, cropped input, reflected/rotated mappings and other unsupported capture contracts remain explicitly rejected. Shared provider fixtures retain full pixels, cold/warm/independent replay and original counters; source transport and raw MIL controls retain invalid-tail rollback and immutable generations.

Stack and evidence

Exact head: 37c3895. Source-only union includes #267 and #270/#271; none is qualified by the merge itself. Independent original Windows reference is #276.

After the major implementation commit, strict C++ syntax passed for the actual MIL implementation/tests and instantiated fixture. The focused managed source host passed 62 cases, with zero failures. Contract freshness and whitespace checks passed. These are not native execution, package or application qualification.

Required before merge

The inherited #271 Windows reference-pipeline crash remains open. The first #276 original Windows run also exposed a UV expectation mismatch, under investigation; no native or Windows padding parity is claimed. Full native Build dispatch is intentionally deferred until the parent crash is resolved to avoid repeating a known failure and duplicating the macOS backlog. A complete successful exact Build, all relevant checks and independent reference resolution remain required before merge or source-host integration. No runtime was staged and WPF source pins are unchanged.