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/form.js

@@ -5,7 +5,8 @@
 
 (function () {
   const NODE_KINDS = ["narration", "dialogue", "choice", "choice_once", "random",
-                      "fight", "move", "anim", "reward", "out_ref"];
+                      "fight", "move", "anim", "reward", "out_ref", "scene"];
+  const SCENE_CLIP_KINDS = ["move", "dialogue", "narration", "anim", "camera", "wait"];
 
   // ---- DOM 小工具 ----
   function el(tag, attrs, kids) {
@@ -252,6 +253,8 @@
       const seqs = (ir.sequences || []).map(s => ({ value: s.id, label: s.id }));
       host.appendChild(field("引用子序列 ref", sel(node.ref, [{ value: "", label: "（无）" }].concat(seqs), v => { node.ref = v; ctx.onChange(false); })));
       host.appendChild(field("出口接回 next", sel(node.next, tgt, v => { node.next = v; ctx.onChange(true); })));
+    } else if (node.kind === "scene") {
+      renderScene(host, ir, node, ctx, tgt);
     }
 
     // 删除节点
@@ -263,6 +266,70 @@
     ]));
   };
 
+  // scene 内 clip 唯一 id
+  function newClipId(node) {
+    let i = 1, id; const has = x => (node.tracks || []).some(tk => (tk.clips || []).some(c => c.id === x));
+    do { id = "c" + i++; } while (has(id));
+    return id;
+  }
+
+  // ========== 演出段 scene 右栏（精确数值编辑，与画布拖拽互补）==========
+  function renderScene(host, ir, node, ctx, tgt) {
+    if (!node.tracks) node.tracks = [];
+    const actorSlots = [{ value: "P1", label: "P1 玩家" }].concat((ir.roles || []).map(r => ({ value: r.slot, label: r.slot + " " + r.name })));
+
+    host.appendChild(el("div", { class: "fld" }, [
+      el("button", { class: "mini primary", onclick: () => ctx.editScene && ctx.editScene(node.id) }, ["🎬 打开时间线编辑器（拖拽编排）"]),
+    ]));
+    host.appendChild(el("div", { class: "row2" }, [
+      field("时长 duration(可选,缺省=自动)", num(node.duration, v => { if (v == null) delete node.duration; else node.duration = v; ctx.onChange(false); })),
+      field("出口 next", sel(node.next, tgt, v => { node.next = v; ctx.onChange(true); })),
+    ]));
+
+    const box = el("div", { class: "subbox" });
+    box.appendChild(el("div", { class: "hd" }, [
+      el("span", {}, ["轨道 tracks"]),
+      el("span", {}, [
+        el("button", { class: "mini", onclick: () => { node.tracks.push({ id: "tk" + node.tracks.length, actor: "P1", clips: [] }); ctx.onChange(true); } }, ["＋演员轨"]),
+        el("button", { class: "mini", onclick: () => { node.tracks.push({ id: "tkcam" + node.tracks.length, role: "camera", clips: [] }); ctx.onChange(true); } }, ["＋镜头轨"]),
+      ]),
+    ]));
+    (node.tracks || []).forEach((tk, ti) => {
+      const isCam = tk.role === "camera";
+      const tbox = el("div", { class: "fld optdet-like" });
+      tbox.appendChild(el("div", { class: "row2" }, [
+        isCam ? el("span", { class: "node-id" }, ["🎬 镜头轨"])
+          : sel(tk.actor || "P1", actorSlots, v => { tk.actor = v; ctx.onChange(false); }),
+        el("span", {}, [
+          el("button", { class: "mini", onclick: () => {
+            const c = { id: newClipId(node), kind: isCam ? "camera" : "move", start: 0 };
+            if (isCam) c.focus = (ctx.pointNames || [])[0] || ""; else c.to = (ctx.pointNames || [])[0] || "";
+            (tk.clips = tk.clips || []).push(c); ctx.onChange(true);
+          } }, ["＋clip"]),
+          el("button", { class: "mini", onclick: () => { if (confirm("删除该轨道？")) { node.tracks.splice(ti, 1); ctx.onChange(true); } } }, ["删轨"]),
+        ]),
+      ]));
+      (tk.clips || []).forEach((c, ci) => {
+        const kinds = isCam ? ["camera"] : SCENE_CLIP_KINDS.filter(k => k !== "camera");
+        const row = el("div", { class: "se-cliprow" }, [
+          sel(c.kind, kinds.map(k => ({ value: k, label: k })), v => { c.kind = v; ctx.onChange(true); }),
+          field("start", num(c.start, v => { c.start = v == null ? 0 : Math.max(0, v); ctx.onChange(false); })),
+          field("dur", num(c.dur, v => { if (v == null) delete c.dur; else c.dur = v; ctx.onChange(false); })),
+        ]);
+        if (c.kind === "move") row.appendChild(field("to", sel(c.to, pointOpts(ir, ctx, c.to), v => { c.to = v; ctx.onChange(false); })));
+        else if (c.kind === "camera") row.appendChild(field("focus", sel(c.focus, pointOpts(ir, ctx, c.focus), v => { c.focus = v; ctx.onChange(false); })));
+        else if (c.kind === "dialogue" || c.kind === "narration") row.appendChild(field("文本", txt(c.text, v => { c.text = v; ctx.onChange(false); })));
+        else if (c.kind === "anim") row.appendChild(field("ani", txt(c.ani, v => { c.ani = v; ctx.onChange(false); })));
+        row.appendChild(el("button", { class: "mini", onclick: () => { tk.clips.splice(ci, 1); ctx.onChange(true); } }, ["✕"]));
+        tbox.appendChild(row);
+      });
+      if (!(tk.clips || []).length) tbox.appendChild(el("div", { class: "empty" }, ["无 clip"]));
+      box.appendChild(tbox);
+    });
+    if (!node.tracks.length) box.appendChild(el("div", { class: "empty" }, ["无轨道——点「＋演员轨/＋镜头轨」"]));
+    host.appendChild(box);
+  }
+
   function renderEnding(host, ir, e, ctx) {
     host.appendChild(field("结局摘要 summary", txt(e.summary, v => { e.summary = v; ctx.onChange(false); })));
     host.appendChild(field("结果 result", sel(e.result || "success", [