revert macro-clips button feature (keep markers + scripts)

The button authoring ended up too far from the intended model after
three correction passes. Pulling it out entirely so we can rebuild
from a clean spec. Markers, script tracks, script frames, the Action
editor, the Script DSL and the runtime for all of the above stay —
they work.

Removed:
- types: ButtonState, StateTransition, ButtonHitArea, ButtonClip,
  ButtonInstance, setButtonState/setButtonDisabled Action variants,
  Scene.buttonClips/buttonInstances
- store: activeButtonClip* getters, all add/remove/setButton* actions,
  seedDefaultButtonClip, enterButtonEdit/setActiveButtonState/
  exitButtonEdit, button-label resolution in actionRuntime
- useButtonRuntime composable, buttonBlend helper,
  ButtonInstanceDialog, sidebar Buttons section, Timeline button
  rendering + pointer handlers, CanvasStage button rendering +
  pointer state machine, exportPlayer button runtime + hit-testing
- DSL commands state/enable/disable and their parse errors
- 35 button-related tests + helpers; stale testing doc; stale design
  doc

Re-applied three uncommitted fixes that were unrelated to the button
work:
- clicking a marker no longer jumps the playhead (only drag / dblclick
  act on it)
- script tracks get a right-click context menu (rename + delete,
  color in the existing palette)
- onTracksPointerDown excludes .script-lane / .script-frame so
  clicks on empty lanes or on frame dots reach the frame-open path
  instead of being swallowed by box-select pointer capture

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

src/components/AssetSidebar.vue

@@ -2,7 +2,6 @@
 import { computed, ref, watch } from 'vue'
 import {
   PhCircle,
-  PhCursorClick,
   PhFilmStrip,
   PhImage,
   PhImageSquare,
@@ -108,7 +107,6 @@ async function addSampleText() {
 }
 
 const clips = computed(() => store.scene.clips ?? [])
-const buttonClips = computed(() => store.scene.buttonClips ?? [])
 
 async function addClip() {
   const input = await promptDialog({
@@ -149,45 +147,6 @@ function onClipDragStart(e: DragEvent, clipId: string) {
   e.dataTransfer.setData('text/plain', clipId)
 }
 
-async function addButtonClip() {
-  const input = await promptDialog({
-    title: t('sidebar.newButtonDialog.title'),
-    message: t('sidebar.newButtonDialog.message'),
-    defaultValue: t('sidebar.newButtonDialog.default'),
-    confirmLabel: t('sidebar.newButtonDialog.confirm'),
-  })
-  if (input === null) return
-  store.seedDefaultButtonClip(input || t('sidebar.newButtonDialog.default'))
-}
-
-async function renameButtonClipPrompt(id: string, current: string) {
-  const input = await promptDialog({
-    title: t('sidebar.renameButtonDialog.title'),
-    defaultValue: current,
-    confirmLabel: t('sidebar.renameButtonDialog.confirm'),
-  })
-  if (input === null) return
-  store.setButtonClipName(id, input)
-}
-
-async function deleteButtonClip(id: string) {
-  const ok = await confirmDialog({
-    title: t('sidebar.deleteButtonDialog.title'),
-    message: t('sidebar.deleteButtonDialog.message'),
-    confirmLabel: t('sidebar.deleteButtonDialog.confirm'),
-    variant: 'danger',
-  })
-  if (!ok) return
-  store.removeButtonClip(id)
-}
-
-function onButtonClipDragStart(e: DragEvent, id: string) {
-  if (!e.dataTransfer) return
-  e.dataTransfer.effectAllowed = 'copy'
-  e.dataTransfer.setData('application/x-animatr-button-clip', id)
-  e.dataTransfer.setData('text/plain', id)
-}
-
 async function handleFileSelected(event: Event) {
   uploadError.value = null
   const input = event.target as HTMLInputElement
@@ -377,51 +336,6 @@ function onAssetDragStart(e: DragEvent, asset: Extract<Asset, { kind: 'image' }>
       </li>
       <li v-if="!clips.length" class="empty">{{ t('sidebar.noClips') }}</li>
     </ul>
-
-    <div class="lib-header clips-header">
-      <h4>{{ t('sidebar.buttons') }}</h4>
-      <button
-        class="thumb-toggle"
-        :title="t('sidebar.createButtonTooltip')"
-        @click="addButtonClip"
-      >
-        <PhPlus :size="12" weight="bold" />
-      </button>
-    </div>
-    <ul class="clips">
-      <li
-        v-for="bc in buttonClips"
-        :key="bc.id"
-        class="clip button-clip"
-        draggable="true"
-        @dragstart="onButtonClipDragStart($event, bc.id)"
-      >
-        <div class="clip-icon">
-          <PhCursorClick :size="16" />
-        </div>
-        <div class="clip-meta">
-          <span class="clip-name" :title="bc.name">{{ bc.name }}</span>
-          <span class="clip-sub">{{ t('sidebar.buttonSubtitle') }}</span>
-        </div>
-        <div class="clip-actions">
-          <button
-            class="clip-btn"
-            :title="t('sidebar.renameTooltip')"
-            @click.stop="renameButtonClipPrompt(bc.id, bc.name)"
-          >
-            <PhPencilSimple :size="11" />
-          </button>
-          <button
-            class="clip-btn danger"
-            :title="t('sidebar.deleteTooltip')"
-            @click.stop="deleteButtonClip(bc.id)"
-          >
-            <PhTrash :size="11" />
-          </button>
-        </div>
-      </li>
-      <li v-if="!buttonClips.length" class="empty">{{ t('sidebar.noButtons') }}</li>
-    </ul>
   </div>
 </template>