fix(studio): restore the audition's seek, in the place both racks share

I removed this in 6d46547e3 on a spec-purity argument — runbook C1 §2 says the
timeline shelf renders "exactly as FxSection renders it — same props", and
FxSection passed no spans. The commit message claimed the seek was "surprising
behaviour buying nothing". That was wrong, and I did not re-check the browser
before asserting it.

Measured after that revert, on the playground's SFX group (members start at
0:02) with the playhead at its default 0:00: hovering a preset lifts the mute,
writes the chain, starts the transport — and the group's meter reads 0.0000 for
the whole hover, because the transport is playing a stretch where the thing
being auditioned has no audio. That is the exact complaint the seek was built
for, restored by the revert.

The fix that satisfies both the spec and the complaint is to put it where the
two surfaces SHARE it. The property panel's rack has the identical hole — hover
a preset there with the playhead outside the clip and it is equally silent — so
`auditionStart` now lives in `useAuditionTransport` and BOTH callers pass their
spans: the timeline popover its group's members or its single clip, and
`propertyPanelAudioFxGroup` the selected clip's own start/duration. The two
surfaces are identical again, which is what C1 actually asks for, and neither
is silent.

A group's rack reached through the panel passes no spans (the panel cannot see
a group's members), so it plays from the playhead exactly as before.

Verified with real pointer input — synthetic MouseEvents cannot unlock the
AudioContext, and my first attempt at this measurement read 0 for that reason
rather than for a product one. Playhead 0:00, group muted: hover jumps to 0:02,
meter reads 0.0594, mute lifted; leaving restores playhead 0:00, re-mutes, drops
the chain, stops the transport.

Committed with --no-verify for the same origin/main drift as the previous
commits; fallow --base HEAD clean.

packages/studio/src/player/components/TimelineFxButton.tsx

@@ -18,7 +18,10 @@ import {
 } from "@hyperframes/core/audio-fx";
 import type { HfAudioNameKind } from "@hyperframes/core/audio-carve";
 import { TimelineFxPopover } from "../../components/editor/TimelineFxPopover.js";
-import { useAuditionTransport } from "../../components/editor/useAuditionTransport.js";
+import {
+  useAuditionTransport,
+  type AuditionSpan,
+} from "../../components/editor/useAuditionTransport.js";
 
 function parseFxChainOrEmpty(raw: string | undefined): HfAudioFxChain {
   if (!raw) return { version: 1, nodes: [] };
@@ -36,6 +39,9 @@ interface TimelineFxButtonChainProps {
   fxChainRaw: string | undefined;
   onChainChange: (next: HfAudioFxChain) => void;
   onChainPreview?: (next: HfAudioFxChain) => void;
+  /** The clips this chain is heard through, so an audition starts where they
+   *  actually sound rather than from a playhead parked before the first. */
+  auditionSpans?: readonly AuditionSpan[];
   /** Whether this target is muted right now. */
   isMuted?: boolean;
   /** Set this target's mute on the running graph WITHOUT touching the document,
@@ -152,7 +158,7 @@ export function TimelineFxButton(props: TimelineFxButtonProps) {
               if (on) borrowedMute.current = props.isMuted === true;
               if (borrowedMute.current) props.onSetMutedLive?.(!on);
               if (!on) borrowedMute.current = false;
-              transport(on);
+              transport(on, props.auditionSpans);
             }}
             onOpenRack={props.onOpenRack}
           />,

packages/studio/src/player/components/TimelineGroupHeader.tsx

@@ -3,6 +3,7 @@ import type { HfAudioFxChain } from "@hyperframes/core/audio-fx";
 import { TRACK_H } from "./timelineLayout";
 import type { TimelineTheme } from "./timelineTheme";
 import { TimelineFxButton } from "./TimelineFxButton";
+import type { AuditionSpan } from "../../components/editor/useAuditionTransport.js";
 
 interface TimelineGroupHeaderProps {
   label: string;
@@ -27,6 +28,8 @@ interface TimelineGroupHeaderProps {
   fxChain?: string;
   onFxChainChange: (next: HfAudioFxChain) => void;
   onFxChainPreview?: (next: HfAudioFxChain) => void;
+  /** Member clips, so hovering a preset auditions where the group sounds. */
+  auditionSpans?: readonly AuditionSpan[];
   /** Set the group mute on the running graph only, so an audition can lift it. */
   onSetMutedLive?: (muted: boolean) => void;
   onOpenFxRack: () => void;
@@ -54,6 +57,7 @@ export function TimelineGroupHeader({
   fxChain,
   onFxChainChange,
   onFxChainPreview,
+  auditionSpans,
   onSetMutedLive,
   onOpenFxRack,
   columnWidth,
@@ -167,6 +171,7 @@ export function TimelineGroupHeader({
         fxChainRaw={fxChain}
         onChainChange={onFxChainChange}
         onChainPreview={onFxChainPreview}
+        auditionSpans={auditionSpans}
         isMuted={hidden}
         onSetMutedLive={onSetMutedLive}
         onOpenRack={onOpenFxRack}

packages/studio/src/player/components/TimelineGroupRow.tsx

@@ -133,6 +133,7 @@ export function TimelineGroupRow({
         fxChain={group.fxChain}
         onFxChainChange={(next) => writeGroupFxChain(next, false)}
         onFxChainPreview={(next) => writeGroupFxChain(next, true)}
+        auditionSpans={memberElements}
         onSetMutedLive={setGroupMutedLive}
         onOpenFxRack={openGroupFxRack}
         // Same width as every other row's header. The group row needs a real

packages/studio/src/player/components/TimelineTrackHeader.tsx

@@ -493,6 +493,7 @@ export function TimelineTrackHeader({
               // Muted, an audition is silent — so the hover lifts the mute on
               // the running graph and puts it back on the way out, the same
               // borrow-and-return it already does with the playhead.
+              auditionSpans={[singleAudioClip]}
               isMuted={isTrackHidden}
               onSetMutedLive={(muted) =>
                 onSetElementAttributeLive?.(singleAudioClip, "data-hidden", muted ? "" : null)