fix(studio): make the volume fader tell the truth about the gain it writes (#3305)

* fix(studio): make the volume fader tell the truth about the gain it writes

The fader travels in dB, so its stops are irrational values; serializing them
through the generic two-decimal numeric formatter collapsed the bottom quarter
of its travel onto "0" — a hard mute — and made the knob jump on release
everywhere below unity. Both panels now use the exact serializer, which
round-trips every integer stop back to itself.

Raise the volume automation lane to the same ceiling the fader reaches.
Clamping the lane at unity meant automating a boosted clip silently discarded
the boost, and the panel disables the fader while a lane owns the level, so
there was no way back. This rescales the lane's vertical axis: unity now sits
a quarter of the way up rather than at the top.

Add audio_volume_tween_overrides_gain. Tween values on `volume` are absolute —
they replace the authored gain rather than scaling it — so a clip carrying both
plays at whatever the tween names, and the fader gives no sign of it. The rule
reuses the tween detector the sibling lane/tween rule already has.

* fix(lint): treat a missing data-volume as unity, not as silence

readAttr returns null when the attribute is absent, and Number(null) is 0 —
finite, and not 1 — so a clip carrying NO data-volume cleared both filters and
was reported as authored at silence. Both halves of that were false: absent
means unity everywhere else in the runtime.

It fired on exactly the case the rule exists to bless. The docs this PR edits
say data-volume is the baseline for elements no tween touches, so a tweened
clip is expected not to carry one — the common audio fade. A warning does not
fail check, but an agent reading the fixHint would have written a gain to
correct a level that was never wrong.

packages/core/src/audioAutomation.ts

@@ -12,6 +12,7 @@
  */
 
 import { getAudioFxDef, type HfAudioFxChain } from "./audioFx.js";
+import { MAX_AUDIO_GAIN } from "./audioGain.js";
 
 export const HF_AUDIO_AUTOMATION_ATTR = "data-automation";
 
@@ -135,8 +136,9 @@ export const PRESET_RANGE: AutomationRange = {
 /**
  * The value range a lane is drawn and clamped against.
  *
- * Volume is linear 0..1, matching `data-volume` and the existing volume
- * envelope machinery — no dB conversion enters the volume path. Everything
+ * Volume is linear over the full authoring gain range, matching `data-volume`
+ * and the existing volume envelope machinery — no dB conversion enters the
+ * volume path. Everything
  * else is read from the effect registry, so a lane can never offer a value the
  * renderer would reject, and the log-scaled knobs sweep the way a DAW's do.
  */
@@ -151,9 +153,15 @@ export interface AutomationRange {
   default: number;
 }
 
+/**
+ * One ceiling for the fader, the lane, the preview transport and the render
+ * mixer. Capping the lane at unity while the fader reached +12 dB made
+ * automating a boosted clip silently discard the boost — and the panel
+ * disables the fader while a lane owns it, so there was no way back.
+ */
 export const VOLUME_RANGE: AutomationRange = {
   min: 0,
-  max: 1,
+  max: MAX_AUDIO_GAIN,
   step: 0.01,
   unit: "",
   label: "Volume",