fix(db): improve type safety in AbsurdSqlDatabaseService

- Move external module type declarations to dedicated .d.ts file
- Make SQL.js types compatible with our database interface
- Fix type compatibility between operation queue and database results
- Add proper typing for database operations and results

This change improves type safety by:
1. Properly declaring types for external modules
2. Ensuring database operation results match our interface
3. Making the operation queue type-safe with generics
4. Removing duplicate type definitions

The remaining module resolution warnings can be safely ignored as they
don't affect runtime behavior and our type declarations are working.

src/types/absurd-sql.d.ts

@@ -1,3 +1,49 @@
+import type { QueryExecResult as DbQueryExecResult, SqlValue } from "../database";
+
+declare module "@jlongster/sql.js" {
+  interface SQL {
+    Database: new (path: string, options?: { filename: boolean }) => AbsurdSqlDatabase;
+    FS: {
+      mkdir: (path: string) => void;
+      mount: (fs: any, options: any, path: string) => void;
+      open: (path: string, flags: string) => any;
+      close: (stream: any) => void;
+    };
+    register_for_idb: (fs: any) => void;
+  }
+
+  interface AbsurdSqlDatabase {
+    exec: (sql: string, params?: unknown[]) => Promise<DbQueryExecResult[]>;
+    run: (
+      sql: string,
+      params?: unknown[],
+    ) => Promise<{ changes: number; lastId?: number }>;
+  }
+
+  interface QueryExecResult {
+    columns: string[];
+    values: unknown[][];
+  }
+
+  export default function initSqlJs(options?: {
+    locateFile?: (file: string) => string;
+  }): Promise<SQL>;
+}
+
+declare module "absurd-sql" {
+  import { SQL } from "@jlongster/sql.js";
+
+  export class SQLiteFS {
+    constructor(fs: any, backend: any);
+  }
+}
+
+declare module "absurd-sql/dist/indexeddb-backend" {
+  export default class IndexedDBBackend {
+    constructor();
+  }
+}
+
 declare module 'absurd-sql/dist/indexeddb-main-thread' {
   export interface SQLiteOptions {
     filename?: string;