feat(sdk): file-backed fs adapter + setTiming GSAP-script sync; add sdk-playground

packages/sdk-playground/.gitignore

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+.hf-versions/
+composition.html
+dist/
+node_modules/

packages/sdk-playground/README.md

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+# @hyperframes/sdk-playground
+
+Interactive browser playground for the `@hyperframes/sdk` API. Open a composition, edit it through the full SDK op surface, watch the preview update live.
+
+## Running
+
+```bash
+bun run --cwd packages/sdk-playground dev
+```
+
+Serves at `http://localhost:5173`. On first load it reads `packages/sdk-playground/composition.html` from disk (if present) or falls back to a built-in demo composition.
+
+## Features
+
+### File persistence
+
+Composition state is persisted to `packages/sdk-playground/composition.html` via a Vite dev-server plugin backed by `@hyperframes/sdk/adapters/fs`. Every save writes a timestamped snapshot to `.hf-versions/composition.html/` (capped at 20). Reload the page and your last state is restored.
+
+### Preview iframe
+
+Full composition rendered in a sandboxed `<iframe>`. Supports:
+
+- **Play / Pause / Seek** via the transport bar
+- **Click-to-select** elements (highlights in the tree and properties panel)
+- **Drag-to-reposition** — drag any element to a new position; on drop the playground calls `comp.setStyle(id, { left, top })`
+
+### Element tree
+
+Lists all non-root elements. Click any row to select it.
+
+### Properties panel
+
+Editable per-element properties for the selected element:
+
+| Section    | SDK op                                                                      |
+| ---------- | --------------------------------------------------------------------------- |
+| Content    | `comp.setText(id, value)`                                                   |
+| Typography | `comp.setStyle(id, { fontSize, fontWeight, color, fontFamily })`            |
+| Box        | `comp.setStyle(id, { top, left, width, height })`                           |
+| Attributes | `comp.element(id).setAttribute(name, value)` — shows all non-internal attrs |
+| Danger     | `comp.element(id).removeElement()`                                          |
+| Animations | `comp.setTiming(id, { start, duration })` — inline form per GSAP tween      |
+
+### Timeline
+
+DAW-style per-element tween blocks. Drag handles to trim start/end; drag body to move. All edits go through `comp.setTiming(id, { start, duration })` which keeps the GSAP script and DOM attributes in sync.
+
+### Ops panel
+
+Full op surface, grouped by feature:
+
+| Section                      | SDK op                                                                            |
+| ---------------------------- | --------------------------------------------------------------------------------- |
+| PreviewAdapter.select()      | `preview.select([id])`                                                            |
+| setStyle                     | `comp.setStyle(id, styles)`                                                       |
+| setText                      | `comp.setText(id, value)`                                                         |
+| addGsapTween                 | `comp.addGsapTween(target, spec)`                                                 |
+| setTiming                    | `comp.setTiming(id, { start, duration })`                                         |
+| setGsapTween                 | `comp.setGsapTween(animId, updates)`                                              |
+| moveElement                  | `comp.moveElement(id, { parent, index })`                                         |
+| setClassStyle                | `comp.dispatch({ type: "setClassStyle", selector, styles })`                      |
+| setAttribute / removeElement | `comp.element(id).setAttribute()` / `.removeElement()`                            |
+| setVariableValue             | `comp.setVariableValue(id, value)`                                                |
+| find(query)                  | `comp.find({ tag, text, name, track })`                                           |
+| selection() proxy            | `comp.selection().setStyle()` / `.removeElement()`                                |
+| listVersions / loadFrom      | `adapter.listVersions()` / `adapter.loadFrom()`                                   |
+| History / inspect            | `comp.undo()`, `comp.redo()`, `comp.can()`, `comp.getOverrides()`, `comp.flush()` |
+
+### Editor modal
+
+Click "Open editor" to view and directly edit the raw composition HTML. Saving re-opens the composition through the SDK.
+
+---
+
+## Planned / not yet wired
+
+- `comp.setTrackVariable(trackId, variableId)` — variable binding per track
+- `comp.addElement(spec)` — create new elements from the UI
+- `comp.duplicateElement(id)` — duplicate with offset
+- Selection multi-select (current: single-select only)
+- Timeline zoom and horizontal scroll for long compositions
+- Version history browser — list/preview/restore past versions inline (API is implemented; UI shows only list + load-oldest)
+- `comp.on('change', cb)` live event log fed from SDK event stream
+- Render to video via `@hyperframes/producer` integration