Feat/skill multi app migration (#378)

* feat(skill): add database migration and Gemini support for multi-app skills

- Refactor skills table from single key to (directory, app_type) composite primary key
- Add migration logic to convert existing skill records
- Support skill installation/uninstallation for Claude/Codex/Gemini independently
- Add new Tauri commands: get_skills_for_app, install_skill_for_app, uninstall_skill_for_app
- Update frontend API and components to support app-specific skill operations

* fix(usage): correct cache token column order in request log table

- Swap cache read and cache creation columns to match data binding
- Add whitespace-nowrap to all table headers for better display

src/lib/api/skills.ts

@@ -19,17 +19,31 @@ export interface SkillRepo {
   enabled: boolean;
 }
 
+export type AppType = "claude" | "codex" | "gemini";
+
 export const skillsApi = {
-  async getAll(): Promise<Skill[]> {
-    return await invoke("get_skills");
+  async getAll(app: AppType = "claude"): Promise<Skill[]> {
+    if (app === "claude") {
+      return await invoke("get_skills");
+    }
+    return await invoke("get_skills_for_app", { app });
   },
 
-  async install(directory: string): Promise<boolean> {
-    return await invoke("install_skill", { directory });
+  async install(directory: string, app: AppType = "claude"): Promise<boolean> {
+    if (app === "claude") {
+      return await invoke("install_skill", { directory });
+    }
+    return await invoke("install_skill_for_app", { app, directory });
   },
 
-  async uninstall(directory: string): Promise<boolean> {
-    return await invoke("uninstall_skill", { directory });
+  async uninstall(
+    directory: string,
+    app: AppType = "claude",
+  ): Promise<boolean> {
+    if (app === "claude") {
+      return await invoke("uninstall_skill", { directory });
+    }
+    return await invoke("uninstall_skill_for_app", { app, directory });
   },
 
   async getRepos(): Promise<SkillRepo[]> {