refactor(frontend): comprehensive architectural optimization and base component extraction

- Standardized table loading logic with enhanced useTableLoader.
- Unified form submission patterns via new useForm composable.
- Extracted common UI components: SearchInput and StatusBadge.
- Centralized common interface definitions in types/index.ts.
- Achieved TypeScript zero-error status across refactored files.
- Greatly improved code reusability and maintainability.

frontend/src/types/index.ts

@@ -2,6 +2,26 @@
  * Core Type Definitions for Sub2API Frontend
  */
 
+// ==================== Common Types ====================
+
+export interface SelectOption {
+  value: string | number | boolean | null
+  label: string
+  [key: string]: any // Support extra properties for custom templates
+}
+
+export interface BasePaginationResponse<T> {
+  items: T[]
+  total: number
+  page: number
+  page_size: number
+  pages: number
+}
+
+export interface FetchOptions {
+  signal?: AbortSignal
+}
+
 // ==================== User & Auth Types ====================
 
 export interface User {
@@ -890,4 +910,4 @@ export interface UpdateUserAttributeRequest {
 
 export interface UserAttributeValuesMap {
   [attributeId: number]: string
-}
+}