feat(video-validation): add lightweight semantic pre-validator contract

[zedarvates]

Summary

Implements the provider-agnostic semantic gate tracked in #41, without bundling ViCLIP weights or adding a hard dependency:

• VideoTextScorer protocol for ViCLIP-like backends;
• SemanticPrevalidator with PASS / ESCALATE / UNCERTAIN;
• fail-safe handling for missing clips, empty specs, provider failures and invalid scores;
• content-hash cache keyed by shot spec + clip bytes;
• external defect signals force escalation even when semantic similarity is high;
• tests cover thresholds, cache, provider errors and defect escalation.

Safety/quality boundary

A semantic PASS is not a final render approval. Structural, identity, temporal and safety validators can still reject/escalate the clip. This module only decides whether a heavy semantic VLM call can potentially be skipped.

Next step

Add an optional ViCLIP-L/14 provider in an environment where the model/runtime is available, then benchmark heavy-VLM calls avoided vs false-PASS rate on the fixed StoryCore clip set.

Tracks #41.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud