Validate all accessibility hardening together

[Blackspirits]

Purpose

Integration-only validation of the accessibility hardening drafts #83, #85, #86 and #87.

The changes now active together are:

• Fail the accessibility sweep when a window cannot open #83: runtime window construction/show failures are test failures instead of silent skips;
• Stop suppressing accessibility-test dispatcher failures #85: pending dispatcher exceptions are no longer suppressed;
• Do not treat empty visual text as an accessibility label #86: empty/whitespace visual text cannot be inferred as an accessible label; intended dynamic relationships are explicit;
• Cover hidden inputs in the accessibility sweep #87: hidden inputs are audited too, with the two mode-dependent gaps it exposed fixed explicitly.

Evidence

Phase 1 combined #86 + #87 on the exact #86 HEAD:

• restore passed
• build passed
• complete solution test suite passed on the first run
• UI suite: 5,152 passed, 9 skipped, 0 failed (5,161 total)
• retry was not used
• validation run: #34771336172

Phase 2 added the fail-closed harness changes from #83 and #85 to the same integration branch:

• restore passed
• build passed
• complete solution test suite passed on the first run
• UI suite: 5,152 passed, 9 skipped, 0 failed (5,161 total)
• retry was not used
• validation run: #34771603365

Acceptance

• full solution restore/build/tests must pass with all four hardenings active;
• AccessibleNamesTests must stay green with stricter inference, hidden-input coverage, window-open failure reporting and unsuppressed dispatcher failures;
• no production changes beyond the already reviewed Do not treat empty visual text as an accessibility label #86 + Cover hidden inputs in the accessibility sweep #87 fixes.

This PR is an audit integration check, not a merge candidate.

[Blackspirits]

Integration validation complete: #83, #85, #86 and #87 are compatible when active together. Full CI #34771603365 passed restore, build and the complete solution suite on the first run; UITests reported 5,152 passed, 9 skipped and 0 failed. Retry was not used. This PR is evidence-only and not a merge candidate.