Fix exact presentation timing and harden openIMIS replay

[abrichr]

Summary

This consolidates the exact presentation-media fix and the guarded openIMIS Standard replay into one reviewed head.

Exact browser presentation media

• encode new presentation derivatives as browser-compatible MP4/H.264
• preserve demuxer presentation timestamps with no B-frame reordering at a 1,000,000-unit track timebase
• bind the declared duration to the final encoded sample end (max(PTS + duration)), rather than stopping at the final sample start
• retain validation compatibility for already-published WebM packs

Guarded openIMIS Standard replay

• use the hardened generic Playwright structural resolver and one-shot DOM actuation guard instead of the legacy point-only override
• retain visible semantic selectors for Material UI inputs while preserving ambiguity, occlusion, frame-context, and record-identity refusal
• revalidate the same Element and complete bounded DOM descriptor after Playwright's actionability trial, admitting only transient framework presentation churn that restores exactly

Evidence

• 53 focused browser/openIMIS/presentation tests passed
• 94 release-boundary, benchmark-environment, and openIMIS tests passed
• actual wheel and sdist passed check_release_consistency.py --validate-dist-dir; no openIMIS/AGPL benchmark material ships
• pinned openIMIS 25.10 synthetic campaign:
  • eligible: 3/3 Standard VERIFIED
  • expired policy: 3/3 Standard HALTED on refuted Tier 1 read-only SQL evidence
  • 0 model calls
  • 0 observed silent incorrect success
  • 0 observed over-halt
• exact verified and halt MP4s passed inventory/privacy checks, exact packet PTS/sample-end/time-base checks, and real headless-Chromium duration/ended playback

Scope

The combined six-file tree contains the presentation exporter/tests and the openIMIS/Playwright hardening/tests. The public media pack remains outside the Python distribution, and the release validator confirms no openIMIS/AGPL fixture payload is present in the wheel or sdist.