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/lib.rs

@@ -28,7 +28,7 @@ mod store;
 mod tray;
 mod usage_script;
 
-pub use app_config::{AppType, McpApps, McpServer, MultiAppConfig};
+pub use app_config::{AppType, InstalledSkill, McpApps, McpServer, MultiAppConfig, SkillApps};
 pub use codex_config::{get_codex_auth_path, get_codex_config_path, write_codex_live_atomic};
 pub use commands::open_provider_terminal;
 pub use commands::*;
@@ -44,6 +44,7 @@ pub use mcp::{
 };
 pub use provider::{Provider, ProviderMeta};
 pub use services::{
+    skill::{migrate_skills_to_ssot, ImportSkillSelection},
     ConfigService, EndpointLatency, McpService, PromptService, ProviderService, ProxyService,
     SkillService, SpeedtestService,
 };