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/lib/scriptDsl.ts

@@ -1,4 +1,4 @@
-import type { Action, ButtonState } from '@/types/scene'
+import type { Action } from '@/types/scene'
 
 export interface ParseError {
   line: number
@@ -10,13 +10,6 @@ export interface ParseResult {
   errors: ParseError[]
 }
 
-const BUTTON_STATES = new Set<ButtonState>([
-  'normal',
-  'hover',
-  'pressed',
-  'disabled',
-])
-
 /**
  * Parse a small line-based DSL into Action[]. Comments start with `//`
  * and each non-empty line is one command. Known commands:
@@ -25,12 +18,6 @@ const BUTTON_STATES = new Set<ButtonState>([
  *   jump <seconds>            (e.g. `jump 2.5`)
  *   jump #<frame>             (e.g. `jump #135`)
  *   jump @<marker>            (e.g. `jump @intro`)
- *   state btn:<label> <state> (state ∈ normal|hover|pressed|disabled)
- *   enable  btn:<label>
- *   disable btn:<label>
- *
- * Button labels are left as-is in `instanceId`. The runtime resolves
- * labels to real instance IDs at eval time.
  */
 export function parseScript(source: string): ParseResult {
   const actions: Action[] = []
@@ -64,12 +51,6 @@ function parseLine(line: string): { action?: Action; error?: string } {
       return ok({ type: 'rewindToLoop' })
     case 'jump':
       return parseJump(tokens)
-    case 'state':
-      return parseState(tokens)
-    case 'enable':
-      return parseEnable(tokens, false)
-    case 'disable':
-      return parseEnable(tokens, true)
     default:
       return { error: `unknown command "${cmd}"` }
   }
@@ -96,33 +77,3 @@ function parseJump(tokens: string[]): { action?: Action; error?: string } {
   if (!Number.isFinite(time)) return { error: `jump: invalid time "${arg}"` }
   return ok({ type: 'jumpTo', time })
 }
-
-function parseButtonRef(token: string): string | null {
-  if (!token.startsWith('btn:')) return null
-  const label = token.slice(4)
-  return label || null
-}
-
-function parseState(tokens: string[]): { action?: Action; error?: string } {
-  if (tokens.length < 3) return { error: 'state: expected `btn:<label> <state>`' }
-  const label = parseButtonRef(tokens[1])
-  if (!label) return { error: `state: expected button ref like btn:<label>, got "${tokens[1]}"` }
-  const state = tokens[2] as ButtonState
-  if (!BUTTON_STATES.has(state)) {
-    return { error: `state: unknown state "${state}"` }
-  }
-  return ok({ type: 'setButtonState', instanceId: label, state })
-}
-
-function parseEnable(
-  tokens: string[],
-  disabled: boolean,
-): { action?: Action; error?: string } {
-  const verb = disabled ? 'disable' : 'enable'
-  if (tokens.length < 2) return { error: `${verb}: missing button ref` }
-  const label = parseButtonRef(tokens[1])
-  if (!label) {
-    return { error: `${verb}: expected button ref like btn:<label>` }
-  }
-  return ok({ type: 'setButtonDisabled', instanceId: label, disabled })
-}