LaserLab v0.5.0: auditable sampling and blinded annotations

[ProhibitedTV]

Summary

• capture media metadata, provenance warnings, raw-source hashes, frame hashes, extraction settings, and expanded source roles
• add deterministic quick/baseline/wide/exhaustive sampling, scene-change sampling, and brightness-aware near-duplicate suppression
• add blinded candidate filters, blind-ID notes/flags, explicit review completion, and annotation export in JSON/HTML/CSV/bundles
• preserve true blinding: sealed reports, manifests, results, and bundles contain no source roles, paths, or labels
• update the five-step dashboard, documentation, screenshots, and v0.5.0 release checklist

Validation

• 13 unit, integration, sampling, provenance, review, and offscreen GUI tests passed
• full compile and git diff --check passed
• sealed report/manifest leak scan: 0 matches
• sealed bundle leak scan: 0 matches
• fixture annotate -> complete -> bundle -> unblind smoke passed
• Windows LaserLab-v0.5.0-windows-x86_64.zip built and verified
• LaserLab.exe --smoke and LaserLabCLI.exe --help passed

Closes #5
Closes #6
Closes #14