fix: replace implicit app inference with explicit selection for Skills import and sync

Skills import previously inferred app enablement from filesystem presence,
causing incorrect multi-app activation when the same skill directory existed
under multiple app paths. Now the frontend submits explicit app selections
via ImportSkillSelection, and schema migration preserves a snapshot of
legacy app mappings to avoid lossy reconstruction.

Also adds reconciliation to sync_to_app (removes disabled/orphaned symlinks)
and MCP sync_all_enabled (removes disabled servers from live config).

src/lib/api/skills.ts

@@ -48,6 +48,12 @@ export interface UnmanagedSkill {
   path: string;
 }
 
+/** 导入已有 Skill 时提交的应用启用状态 */
+export interface ImportSkillSelection {
+  directory: string;
+  apps: SkillApps;
+}
+
 /** 技能对象（兼容旧 API） */
 export interface Skill {
   key: string;
@@ -103,8 +109,10 @@ export const skillsApi = {
   },
 
   /** 从应用目录导入 Skills */
-  async importFromApps(directories: string[]): Promise<InstalledSkill[]> {
-    return await invoke("import_skills_from_apps", { directories });
+  async importFromApps(
+    imports: ImportSkillSelection[],
+  ): Promise<InstalledSkill[]> {
+    return await invoke("import_skills_from_apps", { imports });
   },
 
   /** 发现可安装的 Skills（从仓库获取） */