Centralize native overlay failure policy

[KeyffMS]

Summary

• add NativeCall as the focused authority for critical, transient, and best-effort Win32/Magnification failures;
• require successful overlay opacity, magnifier creation, transform initialization, color-effect application, and self-exclusion filtering;
• diagnose and recover from transient positioning, sizing, and source-update failures by hiding the overlay until a later refresh;
• diagnose cleanup failures without replacing the primary failure;
• document APIs whose Boolean result is not a standard last-error success contract;
• add deterministic unit tests without requiring a live Magnification API;
• update architecture documentation;
• advance product metadata to 0.5.0.33.

Validation

Windows CI must pass the complete build, full regression suite, architecture checks, and self-contained publish validation.

Closes #37