Harden talking-head pipeline: Watch & Propose creative overlays, fix Round 1 gaps

Scene-director rewrite: agent now watches footage, understands content, and proposes
creative overlays (charts, stats, key terms, comparisons) before building anything.
Presents enhancement plan to user for approval before proceeding.

Compose-director fixes from Round 1 verification:
- eye_enhance: now explicitly required, not silently skippable
- Caption positioning: explicit MarginV=160 for 9:16, never center
- Final encode: mandatory with target file size table
- ASR corrections: new Step 2b to scan transcript and build corrections dict
- Overlay compositing: new Step 3b for burning approved graphics onto footage

Asset-director rewrite: generates Remotion overlay assets (callouts, stat cards,
charts, comparisons) from scene plan. Includes overlay type → Remotion cut mapping
table and dark theme requirements.

Bug fixes found during subagent verification:
- remotion_caption_burn.py: fix run_command API, add npx.cmd for Windows
- visual_qa.py: fix run_command API (3 places), Windows /dev/null → NUL

.gitignore

@@ -64,3 +64,4 @@ remotion-composer/public/*
 # Ignore test/scratch compositions in demo-props (keep only curated demos)
 remotion-composer/public/demo-props/test-*
 remotion-composer/public/demo-props/talking-head-*
+remotion-composer/public/demo-props/caption-burn-*