docs: add battle system, conditional routing, key moments, and creators guide docs

docs/guide/CONDITIONAL_ROUTING.md

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+# 条件路由
+
+## 概述
+
+P25 新增。`nextScene` 从单一场景 ID 扩展为**条件路由数组**。
+第一个满足 `conditions` 的场景自动跳转，末尾无条件项作为默认兜底。
+
+## 基本用法
+
+```json
+{
+  "id": "combat_router",
+  "keyMoment": false,
+  "nextScene": [
+    { "conditions": [{ "variable": "enemy_hp", "op": "<=", "value": 0 }], "targetScene": "victory" },
+    { "conditions": [{ "variable": "player_hp", "op": "<=", "value": 0 }], "targetScene": "defeat" },
+    { "targetScene": "combat" }
+  ]
+}
+```
+
+**解读：** 敌人 HP ≤ 0 → 胜利 / 自己 HP ≤ 0 → 战败 / 否则 → 回到战斗场景循环。
+
+## 配合 QTE 使用
+
+```
+QTE 成功 → effects: enemy_hp -= 25
+  → successScene = "combat_router"
+    ├── enemy_hp <= 0 → victory 场景
+    ├── player_hp <= 0 → defeat 场景
+    └── 否则 → 回到 QTE 场景（循环）
+```
+
+## 向后兼容
+
+旧的 `"nextScene": "alone_ending"` 写法**完全不受影响**。引擎自动区分字符串和数组。