feat(timeline): P2 并行编排——scene 多轨编辑器 + 白模重叠预览

剧情 Timeline P2 前端 + 共享内核（与 SGame 源真同步）：
- ir_core/IR_SCHEMA/样张：scene v0.3 + scene 校验 + 导出 gate(D3)，与 SGame 仓逐字一致
- timeline.js：appendScene 按 authored start 铺多轨 clip(自然重叠预览)，move from 同 actor 跨轨续连(D4)；
  drawStage 改逐 actor 查对话→多人气泡同时计时；导出 _clipDur 纯函数；show() 加 startId 参；常量加 CAMERA_DUR
- scene_edit.js(新)：演出段编辑模态——拖 clip 改 start(吸附 0.1s)、拖右缘改 dur、增删 clip/轨道、
  选中属性条精确编辑、客户端轻量 lint(镜像 validate.py)、▶ 预览此段(复用播放核)
- graph.js：scene 节点(KIND_CN/summary/nodeInner 列轨道)+双击进编辑模态
- form.js：右栏 renderScene 精确数值编辑(轨道/clip 的 start/dur/kind/目标)+打开编辑器按钮
- app.py export：捕获 CompileError 并入 report(scene 被拦时不再 500)
- test_scene.js：离线 10 断言全过(重叠确凿/晚 1.5s 起步/from 续连)；gitignore 忽略本地 _localdemo.db

待浏览器目测拖拽编辑落 IR + 白模重叠演出。

web/static/graph.js

@@ -31,6 +31,10 @@
     if (n.kind === "anim")        return ["动画 · " + nameOf(ir, names, n.actor), n.ani || ""];
     if (n.kind === "reward")      return ["奖励结算", ""];
     if (n.kind === "out_ref")     return ["引用子序列", "→ " + (n.ref || "")];
+    if (n.kind === "scene") {
+      const tks = n.tracks || [], nclip = tks.reduce((a, t) => a + ((t.clips || []).length), 0);
+      return ["演出段 (" + tks.length + "轨)", nclip + " clip" + (n.duration ? " · " + n.duration + "s" : "")];
+    }
     if (n.kind === "ending")      return ["★ 结局", n.summary || ""];
     return [n.kind, ""];
   }
@@ -61,7 +65,7 @@
   }
 
   // ---------- 节点 HTML ----------
-  const KIND_CN = { narration: "旁白", dialogue: "对话", choice: "选择", choice_once: "一次性选择", random: "随机", fight: "战斗", move: "走位", anim: "动画", reward: "奖励", out_ref: "引用", ending: "结局" };
+  const KIND_CN = { narration: "旁白", dialogue: "对话", choice: "选择", choice_once: "一次性选择", random: "随机", fight: "战斗", move: "走位", anim: "动画", reward: "奖励", out_ref: "引用", scene: "演出段", ending: "结局" };
   function nodeInner(ir, node) {
     const names = roleNames(ir), end = isEnding(node);
     const kind = end ? "ending" : node.kind;
@@ -85,6 +89,16 @@
       }
       return label + chOpts;
     }
+    // 演出段 scene：列出各轨（演员/镜头）+ clip 数 + 双击编辑提示
+    if (!end && node.kind === "scene") {
+      const tks = node.tracks || [];
+      const lines = tks.slice(0, 4).map(tk => {
+        const who = tk.role === "camera" ? "🎬 镜头" : nameOf(ir, names, tk.actor || "P1");
+        return '<div class="screl">' + esc(who) + ' · ' + ((tk.clips || []).length) + ' clip</div>';
+      }).join("");
+      const more = tks.length > 4 ? '<div class="screl more">…+' + (tks.length - 4) + ' 轨</div>' : "";
+      return label + '<div class="nbody scenebody">' + (lines || '<div class="screl more">（空演出段）</div>') + more + '<div class="schint">双击编辑时间线</div></div>';
+    }
     // 线性 / 单出口：角色（可选）+ 文本
     const sm = summary(ir, names, node);
     const actor = node.speaker || node.actor;
@@ -188,6 +202,14 @@
       editor.on("connectionCreated", info => { if (building) return; handleConnect(info); });
       editor.on("connectionRemoved", info => { if (building) return; handleDisconnect(info); });
       editor.on("nodeRemoved", id => { if (building) return; const ir = dfId2ir[id]; if (ir && cb.onRemove) cb.onRemove(ir); });
+      // 双击 scene 节点 → 打开时间线编辑模态（演出段编排入口）
+      document.getElementById(containerId).addEventListener("dblclick", e => {
+        const nodeEl = e.target.closest && e.target.closest(".drawflow-node");
+        if (!nodeEl) return;
+        const irId = dfId2ir[nodeEl.id.replace("node-", "")];
+        const n = irId && findNode(irId);
+        if (n && n.kind === "scene" && cb.onEditScene) { e.stopPropagation(); e.preventDefault(); cb.onEditScene(irId); }
+      });
       // 键盘 Del：删画布选中节点 → 交给 app 做「缝合删除」；焦点在输入框时放行文本编辑；选中连线时交给 Drawflow
       document.addEventListener("keydown", e => {
         if (e.key !== "Delete" && e.key !== "Backspace") return;