feat(ui): the creator's six corrections

1. Stream Info + YPP rails are YouTube surfaces → new `youtube` token #ff0000. It is documented
   as brand-only: live state stays `primary`, so the two reds never mean the same thing.
2. EDIT toggle: the checked trigger set the SAME colour as the resting face, so clicking it
   changed nothing visible. Resting is now the neutral surface with muted text; armed is blue with
   dark text, and the label follows the fill.
3. Active scene outline is orange again (`attention`) — it marks the scene you work on, not a
   selection; blue made it read as "selected". Live stays red.
4. Scene names wear the same pill as the hotkey chips (black, 10px radius, 8×2 padding), so both
   labels stay readable over any thumbnail.
5. REC / ON-AIR pills and the running stop button read red while armed/live — including test
   mode, where the top bar is gold. New `RecordPillToggle` style (its own template, because
   SegmentToggle hard-codes a transparent face); the stop button's grey `#333` literal is gone.
6. The properties list had `MaxHeight="420"` inside an Auto row, so it scrolled while the window
   had space left. The row is `*` now and the cap is gone.

Guard: UiShellTests pins all six to the markup and names the one that regresses.

DESIGN.md

@@ -57,6 +57,7 @@
 | `success-container` | `#1d5c38` | Success notice surface (success toast) |
 | `warning-container` | `#b8860b` | Warning surface — health banner, warning toast |
 | `test-container` | `#9c6f1c` | Test-stream chrome: the gold top bar and glow |
+| `youtube` | `#ff0000` | **YouTube-branded surfaces only** — the Stream Info and YPP rails, the YouTube account row. Not for state: live stays `primary` |
 
 **The rule:** red means "live or recording" and nothing else. Never a Send button, a delete action,
 a brand flourish, or a general accent — that was the defect in the first Stitch draft.