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-tauri/src/database/schema.rs

@@ -5,6 +5,13 @@
 use super::{lock_conn, Database, SCHEMA_VERSION};
 use crate::error::AppError;
 use rusqlite::Connection;
+use serde::Serialize;
+
+#[derive(Serialize)]
+struct LegacySkillMigrationRow {
+    directory: String,
+    app_type: String,
+}
 
 impl Database {
     /// 创建所有数据库表
@@ -846,12 +853,31 @@ impl Database {
 
         log::info!("开始迁移 skills 表到 v3 结构（统一管理架构）...");
 
-        // 1. 备份旧数据（用于日志）
+        // 1. 备份旧数据（用于日志和后续启动迁移）
         let old_count: i64 = conn
             .query_row("SELECT COUNT(*) FROM skills", [], |row| row.get(0))
             .unwrap_or(0);
         log::info!("旧 skills 表有 {old_count} 条记录");
 
+        let mut stmt = conn
+            .prepare(
+                "SELECT directory, app_type FROM skills
+                 WHERE installed = 1",
+            )
+            .map_err(|e| AppError::Database(format!("查询旧 skills 快照失败: {e}")))?;
+        let snapshot_rows: Vec<LegacySkillMigrationRow> = stmt
+            .query_map([], |row| {
+                Ok(LegacySkillMigrationRow {
+                    directory: row.get(0)?,
+                    app_type: row.get(1)?,
+                })
+            })
+            .map_err(|e| AppError::Database(format!("读取旧 skills 快照失败: {e}")))?
+            .collect::<Result<Vec<_>, _>>()
+            .map_err(|e| AppError::Database(format!("解析旧 skills 快照失败: {e}")))?;
+        let snapshot_json = serde_json::to_string(&snapshot_rows)
+            .map_err(|e| AppError::Database(format!("序列化旧 skills 快照失败: {e}")))?;
+
         // 标记：需要在启动后从文件系统扫描并重建 Skills 数据
         // 说明：v3 结构将 Skills 的 SSOT 迁移到 ~/.cc-switch/skills/，
         // 旧表只存“安装记录”，无法直接无损迁移到新结构，因此改为启动后扫描 app 目录导入。
@@ -859,6 +885,10 @@ impl Database {
             "INSERT OR REPLACE INTO settings (key, value) VALUES ('skills_ssot_migration_pending', 'true')",
             [],
         );
+        let _ = conn.execute(
+            "INSERT OR REPLACE INTO settings (key, value) VALUES ('skills_ssot_migration_snapshot', ?1)",
+            [snapshot_json],
+        );
 
         // 2. 删除旧表
         conn.execute("DROP TABLE IF EXISTS skills", [])