* test(studio): add design-panel QA fixture and triage matrix
Fixture project covering all panel-editable element archetypes,
plus the QA findings matrix from the design-panel bug campaign.
* fix(studio): make canvas selection hit intended elements
- honor author pointer-events:none in hit-testing (was selecting invisible overlays)
- pause playback before mousedown sampling; fall back to hover selection on null resolve
- invalidate committed selection when the active composition changes
- double-click keeps selection and defers to multi-candidate click cycling
* fix(studio): close remaining selection-layer review findings
- hoverSelection fallback now wired at all 3 mousedown call sites (box-click,
blocked-drag, plain overlay click) instead of just the overlay path
- pointer-events override detection reads computed style, not inline style,
so a CSS-class opt-in (not just inline style=) on a descendant is honored
- defensively remove the pointer-events override before the group-fallback
check too, closing a theoretical gap in the no-elementsFromPoint branch
- a click that resolves to nothing (dead-zone / deselect) no longer leaves
playback paused if it was already playing
* fix(studio-server): child-scoped patch operations with batch abort
- PatchOperation gains optional childSelector/childIndex resolved under the matched parent
- pre-pass resolves every op target; any miss aborts the batch with matched:false, no partial write
- style-decl parsing extracted to sourceStyleMutation to stay under the file-size cap
- new ./source-mutation subpath export (mirrors ./finite-mutation)
* fix(studio): per-child patch op builders and persist-seam harness
- buildTextFieldChildLocator indexes over the parent's full same-tag child list
- buildTextFieldChildOperations emits per-field ops for same-shape multi-field edits
- SDK cutover declines child-scoped batches (hfId mapping would hit the parent)
- persist-seam integration harness drives real client ops through patchElementInHtml
* fix(studio): fail closed on unresolved text-field child index
buildTextFieldChildLocator guessed a synthetic field's position by
counting same-tag "child" fields elsewhere in the array whenever
sourceChildIndex was absent. That heuristic is unreachable today (the
count-mismatch guard in buildTextFieldChildOperations already refuses
add/remove edits before it's reached) but would silently locate the
wrong element for a future caller that wires up synthetic-field
support without also computing a real sourceChildIndex. Return null
instead so the caller falls back to the unsupported-structure path.
