refactor: Modularize database page into components and composables

- Extract types to types/database.ts
- Create composables: useDatabaseApi, useDataTable, useQueryExecutor
- Create components: DatabaseSidebar, DataTable, FilterBar, SchemaInfo,
  QueryEditor, QueryColumnsBar, DatabaseStats, TablePagination
- Add horizontal scroll to DataTable with sticky checkbox column
- Configure @ path alias in vite and tsconfig
- Reduce DatabasePage.vue from 1548 to 314 lines

frontend/src/types/database.ts

@@ -0,0 +1,23 @@
+export interface TableInfo {
+  name: string
+  count: number
+}
+
+export interface TableSchema {
+  name: string
+  type: string
+  notnull: boolean
+  pk: boolean
+}
+
+export interface DbStats {
+  size: string
+  tables: number
+  totalRecords: number
+}
+
+export interface PaginationState {
+  currentPage: number
+  pageSize: number
+  totalRecords: number
+}