macro-clips slice 4a: script frame dialog + reusable action editor

- ActionEditor.vue — reusable list editor for Action[]: add/remove/reorder,
  per-type parameter forms (jump to time/frame/marker, set button
  state/disabled, script source). Marker and button dropdowns pull from
  the store's current scene.
- ScriptFrameDialog.vue — modal wrapping ActionEditor plus time and label
  inputs; commits on close, supports deletion.
- Timeline wires the dialog: clicking a script frame opens it for edit,
  clicking the empty script lane creates a new frame at that time and
  opens the editor.
- i18n keys for all action types, parameters, and dialog labels.

Button-authoring UI (definitions + instance placement + properties panel)
is its own slice (4b) — this commit ships script authoring only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/i18n/messages.ts

@@ -359,6 +359,43 @@ export const en = {
       panCanvas: 'Pan canvas',
     },
   },
+  actions: {
+    empty: 'No actions yet. Add one below.',
+    add: 'Add action',
+    remove: 'Remove',
+    moveUp: 'Move up',
+    moveDown: 'Move down',
+    noMarkers: 'No markers defined',
+    noButtons: 'No labeled button instances',
+    type: {
+      play: 'Play',
+      pause: 'Pause',
+      rewindToLoop: 'Rewind to loop start',
+      jumpTo: 'Jump to time',
+      jumpToFrame: 'Jump to frame',
+      jumpToMarker: 'Jump to marker',
+      setButtonState: 'Set button state',
+      setButtonDisabled: 'Set button disabled',
+      script: 'Run script',
+    },
+    param: {
+      time: 'Seconds',
+      frame: 'Frame',
+      marker: 'Marker',
+      button: 'Button',
+      state: 'State',
+      disabled: 'Disabled',
+      source: 'Script source',
+    },
+  },
+  scriptFrameDialog: {
+    title: 'Script frame',
+    time: 'Time (s)',
+    label: 'Label (optional)',
+    labelPlaceholder: 'e.g. intro-end',
+    remove: 'Delete frame',
+    done: 'Done',
+  },
 } as const
 
 export type Messages = typeof en