Plug-ins: Ease Presets moves out of core into a bundled ScriptUI panel

The Ease Presets panel (#254) is modelled on a third-party panel, so,
as with third-party tools in After Effects, it isn't core any more: it
is `extensions/scriptui-panels/Ease Presets.jsx`, a ScriptUI panel
bundled as an optional extension (Window ▸ Ease Presets.jsx), written
only against the public scripting API. Clicking a preset eases every
pair of neighbouring selected keyframes in one undo step (per
dimension, along the motion path for spatial properties, the keys'
other sides as they play); the fields edit the working curve, which the
panel draws; From Keys, Save, Rename and Delete as before. The twelve
built-in curves are unchanged.

Scripting API fixes it needed (After Effects parity):
- `app.settings` lasts between runs (`script_settings.json` in the
  settings folder; `script.settings.get` / `script.settings.save`).
- Per-key methods (`setTemporalEaseAtKey`, `setInterpolationTypeAtKey`,
  `removeKey`, the continuous / auto-Bezier / roving setters) no longer
  change the user's key selection (they selected the key they edited).
- `keyInTemporalEase` / `keyOutTemporalEase` report linear and
  auto-Bezier sides as they play, `keyIn/OutSpatialTangent` the
  tangents the motion path plays.
- `selectedProperties` includes the properties of selected keyframes.
- `isInterpolationTypeValid` is false for Linear / Bezier on values that
  only hold.

Removed from core: Window ▸ Ease Presets, the `keys.easePreset.*`
commands, `engine::ease_presets` and the `ease_presets.json` store,
`keyframe::EaseCurve` (nothing else used it) and the egui panel. User
presets saved by the v0.6.0 panel move into the panel's app.settings
section the first time settings load (the old file is left as is).
Docs: plugins.md (bundled extensions), parity.md, gaps.md G8, agents.md.

Test: app_settings_last_between_runs,
per_key_methods_keep_the_key_selection_and_report_eases_as_they_play,
spatial_tangents_are_reported_as_the_path_plays (each fails before),
the_ease_presets_panel_eases_every_selected_pair_in_one_undo_step,
a_typed_curve_scales_to_each_dimension_and_follows_motion_paths,
user_presets_save_rename_delete_and_persist,
presets_saved_by_the_old_core_panel_carry_over (script, through the
panel's controls), ease_presets_panel_eases_the_selected_keys_from_its_list
(UI: the panel docks and a click on a preset eases the keys).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/plugins.md

@@ -19,7 +19,7 @@ Guide):
 | `Scripts/ScriptUI Panels`: listed at the bottom of the Window menu, dockable like the app's own panels, `this` is the panel | `Scripts/ScriptUI Panels/` in the settings folder (File ▸ Scripts ▸ Install ScriptUI Panel… copies one there), listed at the bottom of the Window menu, docked like any panel, `this` is the panel; the panels open when the app quits open again at the next launch | Same. Where a panel was docked isn't kept: workspace layouts aren't saved between launches |
 | Keyboard shortcuts for scripts (the Keyboard Shortcuts editor lists the scripts of the Scripts folder) | Shortcuts bind to commands and menu entries; the File ▸ Scripts and Window menu entries of scripts aren't offered | Gap |
 | Running a script from the command line (`afterfx -r script.jsx`) | `effectcraft-cli script`, the control channel's and MCP's `script.run` | Same purpose, other entry points |
-| `app.settings` (kept in the preferences between sessions) | Kept for the run only | Gap |
+| `app.settings` (kept in the preferences between sessions) | Kept in `script_settings.json` in the settings folder (`script.settings.get` / `script.settings.save`) | Same |
 | Allow Scripts to Write Files and Access Network | Settings ▸ Scripting & Expressions | Same |
 
 The settings folder is `~/Library/Application Support/EffectCraft` on macOS, `%APPDATA%\EffectCraft`
@@ -84,10 +84,44 @@ Supported controls: `panel`, `group`, `button`, `iconbutton`, `statictext`, `edi
 `tabbedpanel` / `tab` and `image`, with ScriptUI's automatic layout (`orientation`,
 `alignChildren`, `alignment`, `margins`, `spacing`, `preferredSize`), resource strings, event
 handlers (`onClick`, `onChange`, `onChanging`, `onClose`, `addEventListener`) and `onDraw` with
-ScriptUIGraphics. Agents use a panel like a user: `scriptui.list`, `scriptui.get` (its controls),
-`scriptui.click`, `scriptui.set` and `scriptui.close`; every control has the automation id
+ScriptUIGraphics. Mouse events (`mousedown`, `mousemove`…) aren't sent to scripts yet. Agents use
+a panel like a user: `scriptui.list`, `scriptui.get` (its controls), `scriptui.click`,
+`scriptui.set` and `scriptui.close`; every control has the automation id
 `scriptui.<window>.<control id or name>`. The bundled sample `Layer Tools.jsx`
-(`crates/engine/scripts/ScriptUI Panels/`) is a longer example.
+(`crates/engine/scripts/ScriptUI Panels/`) and the Ease Presets extension below are longer
+examples.
+
+## Bundled extensions
+
+Optional tools that ship with EffectCraft but are not part of its core: they are scripts on the
+public scripting API, like the third-party scripts After Effects users install, and are listed
+with the bundled samples (`file.scripts.list` reports them as `extension`). A script of the same
+name in your Scripts folders takes their place.
+
+### Ease Presets (`extensions/scriptui-panels/Ease Presets.jsx`)
+
+Window ▸ Ease Presets.jsx: easing curves kept by name and applied to pairs of neighbouring
+selected keyframes (#254; it was a core panel in v0.6.0). A curve is the out side of a segment's
+first key and the in side of its second, in the Keyframe Velocity dialog's terms: influence in
+percent, and speed relative to the segment's average speed (1 = as fast as a straight line, 0 = at
+rest), so one curve fits any duration and change of value.
+
+* Click a preset to apply it to every pair of neighbouring selected keyframes of each selected
+  property, in one undo step (per dimension, and along the motion path for spatial properties;
+  the keys' other sides keep playing as they did). The keys stay selected, so you can try another.
+* The drawing shows the working curve; type its numbers (Out % and Speed, In % and Speed) and
+  click Apply, or click From Keys to read the curve between the first selected pair.
+* Save keeps the working curve under the typed name (replacing a preset of that name); Rename
+  and Delete act on the selected preset of your own. The twelve built-in presets can't change.
+* User presets are kept with `app.settings` (section `Ease Presets`, key `userPresets`, in
+  `script_settings.json` in the settings folder). Presets saved by the v0.6.0 core panel
+  (`ease_presets.json`) move there the first time a later version loads its settings; the old
+  file is left as it was.
+
+It uses only After Effects' documented scripting API (`comp.selectedProperties`,
+`Property.selectedKeys`, `keyInTemporalEase` / `keyOutTemporalEase`, `setTemporalEaseAtKey` with
+`KeyframeEase`, `setInterpolationTypeAtKey`, `app.settings`, ScriptUI), so it is also a worked
+example of a keyframe tool.
 
 ## Effect plug-ins