fix(scene): 优化 Live 模式请求非预设关卡时的诊断报错信息

当用户在 ?live=1 下请求旷野或迷宫关卡（如冰冷之原 Level 3）时，明确提示该关卡无单体 LvlPrest 预设，引导切换至资源包 (Pack) 模式浏览。

TAG=agy
CONV=2a1934de-30ef-464e-b3f3-fcbcdbbc49f1

src/scene/act-scene.ts

@@ -60,7 +60,7 @@ import { RoofFadeController } from '../render/roofs.ts'
 import { loadCharacterSheet, facingToDirection } from '../game/character.ts'
 import { loadMonsterAtlas, type LoadedMonsterArt } from '../game/monster-art.ts'
 import { resolveMonsterArtSpec } from '../game/monster-mapping.ts'
-import { ACT_NAMES_ZH, sceneNameZh, variantLabelZh } from '../game/level-names-zh.ts'
+import { ACT_NAMES_ZH, LEVEL_NAMES_ZH, sceneNameZh, variantLabelZh } from '../game/level-names-zh.ts'
 import { GameLoop } from '../sim/loop.ts'
 import { KeyboardInput } from '../sim/input.ts'
 import type { SceneEntrance, SceneWarp, SceneWaypoint } from '../game/level-links.ts'
@@ -910,9 +910,23 @@ async function loadLiveRuntime(
 
   const tables = await loadActTables(archives)
   const wantedLevel = param('level', '')
-  const town: LevelInfo = wantedLevel === ''
-    ? resolveActTown(tables, act)
-    : resolveLevel(tables, Number(wantedLevel), act)
+  let town: LevelInfo
+  try {
+    town = wantedLevel === ''
+      ? resolveActTown(tables, act)
+      : resolveLevel(tables, Number(wantedLevel), act)
+  } catch (err) {
+    if (wantedLevel !== '') {
+      const id = Number(wantedLevel)
+      const nameZh = LEVEL_NAMES_ZH[id] ?? `关卡 ${wantedLevel}`
+      throw new Error(
+        `直读归档 (Live) 模式仅支持预设单体地图（如城镇、大教堂、崔斯特瑞姆等）；` +
+        `${nameZh}（Level ${wantedLevel}）属于由 DRLG 动态拼装生成的旷野/迷宫关卡，在 MPQ 中没有单一 DS1 预设（无 LvlPrest 记录）。` +
+        `请去掉 URL 中的 ?live=1 参数，使用资源包 (Pack) 模式加载完整生成的地图。`
+      )
+    }
+    throw err
+  }
   const wantedVariant = wantedQuadrant || param('variant', '')
   const variants = town.ds1Names.map(name => name.split('\\').pop() ?? name)
   let index = 0