feat(analysis): add pre-render narration sync gate

[RayJiang4S]

Summary

• Add pre_render_narration_sync_gate for checking locked narration against captions, screen text, terminology, and planned visual cue timing before final rendering.
• Write machine-readable results plus Markdown/HTML review artifacts with recommended next actions: ready_to_render, agent_review_required, or revise_before_render.
• Document the workflow and add focused tests for clean, warning, and deterministic-failure paths.

Tests

• .venv/bin/python -m pytest tests/tools/test_pre_render_narration_sync_gate.py
• Registry discovery smoke: registry.get('pre_render_narration_sync_gate')