feat(timeline): 无点位集时合成圆周布局兜底 + 演示事件

- 线上 NAS 多半没挂点位集卷(/api/pointsets 空)，白模会无坐标。改为：真实锚点优先，
  缺坐标时把引用到的点位(演员位/走位目标/镜头点)在圆周自动铺开，走位预览不空。
  真实坐标存在时一律覆盖合成。mapinfo 标注当前是真实坐标还是示意布局。
- samples/timeline_demo.ir.json：QY_TLDEMO 演示事件，覆盖 P1 全部功能
  (旁白/对话打字机/3角色走位/动画标记/镜头对焦/选择分支/双结局)，离线测试合成布局走位全有位移

samples/timeline_demo.ir.json

@@ -0,0 +1,30 @@
+{
+  "id": "QY_TLDEMO",
+  "title": "演出预览功能演示",
+  "theme": "P1 白模演出测试（走位/对话打字机/动画/镜头/多角色）",
+  "scale": "演示",
+  "roles": [
+    { "slot": "NP1", "name": "神秘剑客", "archetype": "负伤外门高手", "camp": 0 },
+    { "slot": "NP2", "name": "客栈小二", "archetype": "市井路人", "camp": 0 }
+  ],
+  "stage": { "type": "客栈·夜", "point_set": "QY_TLDEMO" },
+  "nodes": [
+    { "id": "n_open", "kind": "narration", "speaker": "P1", "text": "夜色深沉，雨点敲打着客栈的窗棂。一道人影立在门外，迟迟没有进来。", "next": "n_p1walk" },
+    { "id": "n_p1walk", "kind": "move", "actor": "P1", "to": "PT_DOOR", "next": "n_p1say" },
+    { "id": "n_p1say", "kind": "dialogue", "speaker": "P1", "text": "（这客栈看着冷清，却处处透着古怪……）", "next": "n_npenter" },
+    { "id": "n_npenter", "kind": "move", "actor": "NP1", "to": "PT_CENTER", "next": "n_npsay" },
+    { "id": "n_npsay", "kind": "dialogue", "speaker": "NP1", "camera": "NP1", "text": "阁下，留步。在下身负旧伤，想借贵宝地歇一晚，天明即走。", "next": "n_draw" },
+    { "id": "n_draw", "kind": "anim", "actor": "NP1", "ani": "draw_sword", "next": "n_p1ask" },
+    { "id": "n_p1ask", "kind": "dialogue", "speaker": "P1", "text": "来者何人？这般夜半叩门，又突然按剑，意欲何为？", "next": "n_xiaoer" },
+    { "id": "n_xiaoer", "kind": "move", "actor": "NP2", "to": "PT_SIDE", "next": "n_xsay" },
+    { "id": "n_xsay", "kind": "dialogue", "speaker": "NP2", "text": "二位客官息怒！有话好好说，小店实在经不起折腾啊……", "next": "n_choice" },
+    { "id": "n_choice", "kind": "choice", "options": [
+      { "text": "收剑，请他进来歇脚", "goto": "end_peace" },
+      { "text": "拔剑相向，喝令他离开", "goto": "end_fight" }
+    ] }
+  ],
+  "endings": [
+    { "id": "end_peace", "summary": "化干戈为玉帛，与剑客结为知己", "grants": [], "result": "success" },
+    { "id": "end_fight", "summary": "不欢而散，剑客消失在茫茫雨夜中", "grants": [], "result": "end" }
+  ]
+}