test(producer): regenerate sub-comp-t0 baseline + improve visual contrast

The text-rendering:geometricPrecision rule (b7bd9565) shifted glyph advances
~1% in headless Chrome. Baselines for png-sequence, heygen-promo-preview-assets,
and sub-composition-video were already regenerated — sub-comp-t0 was missed.

Also improves the fixture's visual contrast:
- Background: #07110d (near-black) → #0f172a (slate-900)
- Hook scene: background #1e293b, text #ef4444/#ffffff
- Later scene: background #334155, text #ffffff
- Absolute positioning for text elements (compiler inlines sub-comp
  content at intrinsic width, collapsing the flex container)

Baseline regenerated inside Dockerfile.test per CLAUDE.md. Test passes:
0 failed frames, 100/100 checkpoints green.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/producer/tests/sub-comp-t0/src/index.html

@@ -15,14 +15,14 @@
         width: 1920px;
         height: 1080px;
         overflow: hidden;
-        background: #07110d;
+        background: #0f172a;
       }
       #root {
         position: relative;
         width: 1920px;
         height: 1080px;
         overflow: hidden;
-        background: #07110d;
+        background: #0f172a;
       }
       .scene {
         position: absolute;