Merge origin/main into the audio stack

Twelve of the stack's feature commits landed on main as squashes (#3274
through #3292, plus #3401's canary removal); the 96 review-and-fix commits
that followed them here did not, and main moved 64 commits on in the
meantime. This reconciles the two.

58 files conflicted. 44 were audio-only — main's side there is the
squashed form of commits this branch already carries and has since
superseded, so the branch side stands. The rest needed real work, in both
directions:

**Taken from main, absent here.**
- `ensureAudioGroupInertStyle` (#3278's review). An `<hf-audio-group>` is
  an unknown custom element, so it still takes a flex/grid slot and can
  open a line box — adding a group shifted authored layout. The helper and
  its `init.ts` call never came back to the branch, and this branch is
  what emits the element.
- `#3383`'s ended-audio replay: `canSeekEndedMediaBackward` and its five
  siblings in `media.ts`, with all six tests. Not present here in any
  form.
- `#3380`'s `asetpts=N/SR/TB` between `apad` and `atrim`. Also applied to
  `mixGroupMembers`, the group submix, which is new on this branch and so
  had the same bug in a path main's fix could not reach: delayed members
  padded then amix'd, where a group of four or more silently loses one.
- `#3401`'s `displayNumber` thread. The header derives its row from the
  group-aware order and the undo label from ascending element keys, so
  once a group exists the same click said "Hide track 2" and recorded
  "Hide track 1".
- `#3413`/`#3421`'s viewport handling — the popover's height cap and
  `inset()`, and `resolveFloatingPanelPosition` for the grouping dialog,
  which lives in a track header at the bottom of the window.
- Two extractions this branch had inline and at exactly the 600-line cap:
  `useTimelineDeleteOps` and `editingModeSlice`. Bodies were identical.

**Kept from the branch, against main.** Mute and solo are gone by
deliberate breaking change (`remove mute and solo from tracks and groups`,
`remove the group volume slider and level meter`), so eight files main
still carries are deleted again, `PlayerControls` keeps no
`previewIframeRef` (it existed only to feed `SoloBanner`), the
group-levels branch comes out of main's new `previewMessageRouter`, and
`STRIP_H` goes with the bus strip it sized. Main's
`TimelineTrackPlainHeader.test.tsx` is rewritten against the control that
actually exists — the visibility eye, withheld from an audible audio row
and offered back once hidden, which is the only way out of `data-hidden`.

**Unioned.** `TimelineFxPopover` — main's positioning, this branch's
audition telemetry (`auditionPresetChain`, `storedChain`,
`onAuditionTracked`); `SKILL.md` — main's #3416 "keep the carve group a
voice group" beside this branch's bus section, with the canary paragraph
dropped since the canaries no longer exist.

Every port is mutation-checked. core 2508, studio 4460, lint 528, engine
1630, cli 2813, sdk 549, producer green; tsc, oxlint, oxfmt, fallow and
the 600-line cap clean.

README.md

@@ -38,12 +38,12 @@ HyperFrames is an open-source framework for turning HTML, CSS, media, and seekab
 Install the HyperFrames skills, then describe the video you want:
 
 ```bash
-npx skills add heygen-com/hyperframes --full-depth
+npx skills add heygen-com/hyperframes
 ```
 
 > The picker opens with nothing pre-selected — the **Core Skills** group is all you need: the `/hyperframes` router installs each creation workflow on demand. Agents and non-interactive runs should use `npx hyperframes skills update` instead — it installs exactly the core set, whereas a non-interactive `skills add` without `--skill` installs all 20.
 >
-> `--full-depth` does a full clone of the repo's current `main`. Without it, `skills add` fetches the skills.sh registry blob, which lags `main` by hours — you'd get an older copy of a skill. (`hyperframes skills update` already installs full-depth.)
+> `skills add` resolves the skills.sh registry blob, which can lag `main` by hours. `npx hyperframes skills update` installs from the current `main`, so reach for it when you need the newest copy of a skill.
 
 Try a prompt like:
 
@@ -55,7 +55,7 @@ The skills teach agents the HyperFrames production loop: plan the video, write v
 
 HyperFrames ships 20 skills agents load on demand. Read `/hyperframes` first — it's the router and capability map; it picks a workflow for any "make me a…" request — video, deck, or composition port — and points to the domain skills below.
 
-Default to the **core set** — the router installs each creation workflow on demand. `npx hyperframes skills update` installs exactly that from anywhere; the interactive picker (`npx skills add heygen-com/hyperframes --full-depth`) lists it as the "Core Skills" group, nothing pre-selected. The picker is interactive-only — a non-interactive or agent run without `--skill` installs all 20. Use `npx skills add heygen-com/hyperframes --all --full-depth` to install all 20 deliberately (skips the picker), or `npx skills add heygen-com/hyperframes --skill <name> --full-depth` for just one (bare name, no leading `/`). Keep `--full-depth` — it installs the current `main`; without it `skills add` fetches the skills.sh blob, which lags by hours.
+Default to the **core set** — the router installs each creation workflow on demand. `npx hyperframes skills update` installs exactly that from anywhere; the interactive picker (`npx skills add heygen-com/hyperframes`) lists it as the "Core Skills" group, nothing pre-selected. The picker is interactive-only — a non-interactive or agent run without `--skill` installs all 20. Use `npx skills add heygen-com/hyperframes --all` to install all 20 deliberately (skips the picker), or `npx skills add heygen-com/hyperframes --skill <name>` for just one (bare name, no leading `/`).
 
 Installs stay lean after that: `npx hyperframes init` keeps the **core set** fresh (the router, the `hyperframes-*` domain skills, and `media-use` — plus whatever is already installed; `/figma` stays on demand) and never expands a partial install; the creation workflows install **on demand** — the router runs `npx hyperframes skills update <workflow>` before entering one. Nothing re-pulls the full set behind your back.