feat(studio): timeline revamp with active-clip highlighting and hide controls (#2017)

Timeline UI
- Highlight clips visible at the playhead in the primary color; others share one neutral color
- Minimalist rounded clips, single-color track rows, no gutter icons or superscript labels
- Per-track eye toggle and a per-element hide button in the design panel
- Ruler zoom fixes: sub-second tick intervals and correct label formatting at high zoom
- Sticky gutter so track controls stay visible while scrolling

WYSIWYG visibility (data-hidden)
- Runtime honors data-hidden (display:none), so hiding affects the render, not just the preview
- HTML stays the source of truth; hide state persists and round-trips on reload

Split several studio files to stay under the 600-line cap; pure relocations, no behavior change.

skills/hyperframes-core/SKILL.md

@@ -64,6 +64,7 @@ Surfaced here; full rationale in the linked reference. Do not violate:
 - Read the files first. Preserve unrelated timing, tracks, IDs, variables, media paths.
 - Match existing composition IDs and timeline keys.
 - Adding a clip: pick a non-overlapping `data-track-index` or adjust surrounding timing intentionally.
+- `data-hidden` on any composition element hides it in BOTH preview and render, overriding its time window; it is non-destructive/reversible and toggled by Studio's timeline eye icon.
 - Adding a sub-composition: verify its internal `data-composition-id` before wiring the host.
 
 ## Validation