fix(studio): resolve 8 confirmed adversarial-review findings across the flat-inspector stack

Fixes issues raised in the Deepwork re-review of #2120-#2190 that weren't
covered by #2225's earlier fix pass:

- useColorGradingController: reset grading/compare/mediaMetadata state (and
  cancel pending persist/status timers) when selection changes to a
  different element — this hook is called unconditionally on every render
  (unlike legacy ColorGradingSection, remounted via a selectionIdentityKey
  React key), so switching selection reused the previous element's state.
- useColorGradingController: stop permanently caching a non-OK
  /media/metadata response as null — a transient server error poisoned the
  HDR banner for that asset for the whole page lifetime.
- FlatSelectRow: preserve a valid authored value outside the preset list
  (e.g. mix-blend-mode: difference, an arbitrary object-position) instead of
  silently misrepresenting it as the first preset — touching the control
  would overwrite real persisted state.
- FlatSlider: the throttled trailing commit now reads onCommit through a
  ref updated every render instead of closing over it at schedule time — a
  caller whose onCommit spreads other current state (Grade's per-detail
  commits) could otherwise have a delayed commit revert whatever the user
  changed on a different control in the same 40ms window.
- FlatSlider: flush a still-queued trailing commit on unmount instead of
  dropping it, and disable the reset button when the slider itself is
  disabled.
- FlatSlider: add touch-action: none to the track so touch drags don't
  compete with page scroll.
- FlatColorGradingAccessory: clean up the compare-hold's window listeners
  on unmount, not only on release — switching selection mid-hold used to
  leak them.
- Align (flat Text): re-clicking the option already visually active for a
  logical start/end value no longer rewrites it to the physical left/right,
  preserving RTL semantics.
- FlatSegmentedRow: give every option an accessible name and aria-pressed
  state — two visually-identical glyph buttons (upright/italic "A") had no
  way to be told apart by assistive tech.
- PropertyPanelFlat: the panel body falls back to its own scroll when the
  collapsed group headers alone exceed the available height, so groups
  can't become permanently unreachable in a short pane.

New regression tests for all of the above; full studio suite at the known
pre-existing baseline (55 failures unrelated to this stack).

packages/studio/src/components/editor/propertyPanelFlatLayoutSection.tsx

@@ -203,8 +203,8 @@ export function LayoutFlexBlock({
       <FlatSegmentedRow
         label="Direction"
         options={[
-          { key: "row", node: "→ Row", active: direction === "row" },
-          { key: "column", node: "Column", active: direction === "column" },
+          { key: "row", node: "→ Row", label: "Row", active: direction === "row" },
+          { key: "column", node: "Column", label: "Column", active: direction === "column" },
         ]}
         disabled={disabled}
         onChange={(next) => void onSetStyle("flex-direction", next)}