fix(producer): correct short VFR frame coverage

[jrusso1020]

Summary

• Use one shared extraction frame-count calculation so VFR extraction and coverage expectations both use ceil while CFR continues to use round.
• Allow exactly one missing frame only for short 14 through 20 frame clips when the configured threshold is below 1.
• Preserve fail-closed behavior for missing media, zero captured frames, 1 of 2, deficits of two or more, longer clips, and exact-threshold mode.

Acceptance cases

• 13 of 14 and 18 of 19 pass under the bounded tolerance.
• 0 of 19, 17 of 19, 1 of 2, larger deficits, and threshold=1 fail.
• Real VFR superset extraction produces the expected 19 frames.

Validation

• Targeted coverage and extractor suites: 114 passing.
• Full engine suite: 1,237 passing, 3 skipped.
• Full producer unit lane: 456 Vitest tests plus all Bun unit files passing.
• Full producer integration lane: all Vitest and Bun integration files passing.
• Pre-commit tracked-artifact, lint, format, fallow, and typecheck gates passing.
• Independent adversarial review: no blockers.

Scope

HDR behavior and hyperframes-internal dependency or version changes are intentionally out of scope.

Rollback

Revert commit 8105516. No migration or persisted state is introduced.