refactor(types): rename AppType to AppId for semantic clarity

Rename `AppType` to `AppId` across the entire frontend codebase to better
reflect its purpose as an application identifier rather than a type category.
This aligns frontend naming with backend command parameter conventions.

Changes:
- Rename type `AppType` to `AppId` in src/lib/api/types.ts
- Remove `AppType` export from src/lib/api/index.ts
- Update all component props from `appType` to `appId` (43 files)
- Update all variable names from `appType` to `appId`
- Synchronize documentation (CHANGELOG, refactoring plans)
- Update test files and MSW mocks

BREAKING CHANGE: `AppType` type is no longer exported. Use `AppId` instead.
All component props have been renamed from `appType` to `appId`.

src/lib/api/usage.ts

@@ -1,12 +1,12 @@
 import { invoke } from "@tauri-apps/api/core";
 import type { UsageResult } from "@/types";
-import type { AppType } from "./types";
+import type { AppId } from "./types";
 
 export const usageApi = {
-  async query(providerId: string, appType: AppType): Promise<UsageResult> {
+  async query(providerId: string, appId: AppId): Promise<UsageResult> {
     return await invoke("query_provider_usage", {
       provider_id: providerId,
-      app: appType,
+      app: appId,
     });
   },
 };