Sound: per-node scene music + synthesized SFX (zero-dep)

- migration 023: story_nodes.music_asset_id (references the asset store).
- src/audio.ts: a tiny audio manager — one looping scene-music track (fade,
  dedup, gesture-primed autoplay) and synthesized one-shot SFX; global mute.
- Runtime: RuntimeNode.musicUrl; music follows the current node (null inherits,
  a finished playthrough stops). SFX blips on dialogue advance/choice (not in the
  editor preview). Floating mute toggle during play.
- Graph inspector: a "Scene music" picker sourced from uploaded audio assets.

No external library (we did not adopt react-winamp — it is a React 16 CRA app,
not an installable package). Bundle grew ~2 KB.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/storyGraphRepository.ts

@@ -13,7 +13,7 @@ export type StoryNodeType = 'cutscene' | 'dialogue' | 'level' | 'det_gate' | 'll
 export type TerminalDto = { id: string; terminalKey: string; label: string; toNodeId: string | null; sortOrder: number }
 export type StoryNodeDto = {
   id: string; nodeType: StoryNodeType; label: string; hasUtterances: boolean
-  xpos: number; ypos: number; levelTemplateVersionId: string | null; componentKey: string | null
+  xpos: number; ypos: number; levelTemplateVersionId: string | null; componentKey: string | null; musicAssetId: string | null
   terminals: TerminalDto[]
 }
 export type StoryGraphDto = { mysteryId: string; entryNodeId: string | null; nodes: StoryNodeDto[] }
@@ -37,7 +37,7 @@ const DEFAULT_TERMINALS: Record<StoryNodeType, { key: string; label: string }[]>
 export interface StoryGraphRepository {
   getGraph(mysteryId: string): Promise<StoryGraphDto | null>
   createNode(mysteryId: string, input: { nodeType: StoryNodeType; xpos: number; ypos: number; label?: string }): Promise<StoryNodeDto | null>
-  updateNode(nodeId: string, input: Partial<{ label: string; xpos: number; ypos: number; hasUtterances: boolean; componentKey: string | null; levelTemplateVersionId: string | null }>): Promise<StoryNodeDto | null>
+  updateNode(nodeId: string, input: Partial<{ label: string; xpos: number; ypos: number; hasUtterances: boolean; componentKey: string | null; levelTemplateVersionId: string | null; musicAssetId: string | null }>): Promise<StoryNodeDto | null>
   deleteNode(nodeId: string): Promise<boolean>
   addTerminal(nodeId: string, input: { terminalKey: string; label?: string }): Promise<StoryNodeDto | null>
   updateTerminal(terminalId: string, input: Partial<{ label: string; sortOrder: number; toNodeId: string | null }>): Promise<{ ok: boolean; error?: string }>
@@ -61,8 +61,8 @@ export function createStoryGraphRepository(pool: Pool): StoryGraphRepository {
     const mystery = await pool.query<{ id: string; entry_node_id: string | null }>('SELECT id,entry_node_id FROM osint.mysteries WHERE id=$1', [mysteryId])
     if (!mystery.rows[0]) return null
     const [nodes, terminals] = await Promise.all([
-      pool.query<{ id: string; node_type: StoryNodeType; label: string; has_utterances: boolean; xpos: number; ypos: number; level_template_version_id: string | null; component_key: string | null }>(
-        'SELECT id,node_type,label,has_utterances,xpos,ypos,level_template_version_id,component_key FROM osint.story_nodes WHERE mystery_id=$1 ORDER BY created_at', [mysteryId]),
+      pool.query<{ id: string; node_type: StoryNodeType; label: string; has_utterances: boolean; xpos: number; ypos: number; level_template_version_id: string | null; component_key: string | null; music_asset_id: string | null }>(
+        'SELECT id,node_type,label,has_utterances,xpos,ypos,level_template_version_id,component_key,music_asset_id FROM osint.story_nodes WHERE mystery_id=$1 ORDER BY created_at', [mysteryId]),
       pool.query<{ id: string; parent_node_id: string; terminal_key: string; label: string; to_node_id: string | null; sort_order: number }>(
         `SELECT t.id,t.parent_node_id,t.terminal_key,t.label,t.to_node_id,t.sort_order FROM osint.story_node_terminals t
          JOIN osint.story_nodes n ON n.id=t.parent_node_id WHERE n.mystery_id=$1 ORDER BY t.sort_order,t.terminal_key`, [mysteryId]),
@@ -77,7 +77,7 @@ export function createStoryGraphRepository(pool: Pool): StoryGraphRepository {
       mysteryId, entryNodeId: mystery.rows[0].entry_node_id,
       nodes: nodes.rows.map(row => ({
         id: row.id, nodeType: row.node_type, label: row.label, hasUtterances: row.has_utterances,
-        xpos: row.xpos, ypos: row.ypos, levelTemplateVersionId: row.level_template_version_id, componentKey: row.component_key,
+        xpos: row.xpos, ypos: row.ypos, levelTemplateVersionId: row.level_template_version_id, componentKey: row.component_key, musicAssetId: row.music_asset_id,
         terminals: byNode.get(row.id) || [],
       })),
     }
@@ -117,6 +117,7 @@ export function createStoryGraphRepository(pool: Pool): StoryGraphRepository {
       if (input.hasUtterances !== undefined) set('has_utterances', input.hasUtterances)
       if (input.componentKey !== undefined) set('component_key', input.componentKey || null)
       if (input.levelTemplateVersionId !== undefined) set('level_template_version_id', input.levelTemplateVersionId || null)
+      if (input.musicAssetId !== undefined) set('music_asset_id', input.musicAssetId || null)
       if (sets.length) await pool.query(`UPDATE osint.story_nodes SET ${sets.join(',')} WHERE id=$1`, values)
       const graph = await loadGraph(mysteryId)
       return graph?.nodes.find(node => node.id === nodeId) ?? null