refactor(tests): move backend tests into src/backend/tests mirror tree

Backend *.test.ts files (and the test-support harness) no longer sit next
to source files; they live under src/backend/tests/ mirroring the source
layout. Imports rewritten accordingly; CLAUDE.md convention updated.

src/backend/tests/database/repositories/test-support.ts

@@ -0,0 +1,31 @@
+import Database from "better-sqlite3";
+import { drizzle } from "drizzle-orm/better-sqlite3";
+import * as schema from "../../../database/db/schema.js";
+import type { DatabaseContext } from "../../../database/repositories/database-context.js";
+
+export class TestSqliteDatabase {
+  private sqlite: Database.Database | null = null;
+  private context: DatabaseContext | null = null;
+
+  async connect(): Promise<DatabaseContext> {
+    if (this.context) return this.context;
+
+    this.sqlite = new Database(":memory:");
+    this.sqlite.exec("PRAGMA foreign_keys = ON");
+    this.context = {
+      dialect: "sqlite",
+      drizzle: drizzle(this.sqlite, { schema }),
+      sqlite: this.sqlite,
+    };
+
+    return this.context;
+  }
+
+  async close(): Promise<void> {
+    if (this.sqlite) {
+      this.sqlite.close();
+      this.sqlite = null;
+      this.context = null;
+    }
+  }
+}