Fix historical Reel Retina backfill and spotlight highlighting

[Happy (huangyangyu)]

Summary

• Preserve the canonical DPR1 poster PNG and historical poster HTML while generating quality-gated 2x/3x raster sources from the canonical PDF.
• Install Retina assets and rewritten HTML transactionally, and enable the fallback only for one uniquely identified historical layer inside the marked pixel host.
• Restore historical raster highlighting as a neutral 2px white spotlight with the surrounding poster faded; native HTML posters retain the existing DOM highlight path.
• Harden package QA for srcset/currentSrc, Retina rendering, proxy visibility and pixel effects, focus-core preservation, exact restoration, duplicate IDs, and failed-install recovery.

Retina sources are enabled only when PDF-derived output passes MAE <= 6, RMS <= 14, and maximum 32x32 tile RMS <= 30.

Validation

• Full public Daily Paper catalog repair: 55/55 unique Reels passed HTTP and file:// QA with 0 errors and 0 warnings.
• Public route reconciliation: 55/55 Reel pages and 55/55 nested posters returned HTTP 200; all 165 DPR1/2/3 raster URLs returned HTTP 200 with the expected PNG size.
• Every catalog entry passed all 8 artifact gates and exposed the neutral spotlight plus high-DPR image-rendering: auto runtime, with a unique scoped historical layer and canonical 1x src plus 1x/2x/3x srcset.
• Canonical DPR1 PNG and PDF hashes remained unchanged for all 55 papers. No active transaction journals, hidden staging directories, publisher processes, or scratch directories remained after the batch.
• Targeted production verification for 2608.10915 and 2608.12307: 0 errors, 0 warnings; public DPR1/2/3 and spotlight behavior verified.
• Real 2608.06867 HTTP/file QA at DPR1/2/3: 0 errors.
• Real 2608.10299 full HTTP/file QA: 0 errors, 0 warnings.
• Three real native HTML posters: no hover, flash, or backfill regression.
• Negative coverage passed for localized corruption, wrong/missing PDF, oversized images, partial generation, transaction rollback, duplicate IDs, and full-focus washout.
• Independent final validation passed against merge-base 739f47f: only the two intended paper2reel scripts differ; static checker, focused parser/spotlight assertions, py_compile, both CLI help smoke tests, and git diff --check passed.

No test files, screenshots, reports, generated QA artifacts, or production bundles are included in this PR.