refactor: migrate backend to pnpm monorepo with Hono module architecture

- Replace Bun with pnpm 9 + Turborepo + tsx; apps/api renamed to apps/backend
- Split backend into http/, modules/, lib/ layers mirroring tai-specguard
- Add use-case + Result pattern, Problem Details RFC 7807, basePath /api/v1
- Mount Better Auth at /api/v1/auth, keep session-auth whitelist
- Split Prisma schema into prisma/models/*, generate into generated/
- Rework packages/shared into lib/ + schemas/ with pagination DTOs
- Implement health, groups, students, payments, waitlist modules
- Add vitest suite with prisma mocks (21 tests), biome lint
- Point web client to /api/v1/auth and /api/v1/groups/from-organization

apps/backend/src/modules/groups/features/get-all/use-case.ts

@@ -0,0 +1,51 @@
+import type { Prisma } from '@generated/prisma/client';
+import type {
+  GroupList,
+  GroupQuery,
+  ProblemDetails,
+  Result,
+} from '@gruperly/shared';
+import { ok } from '@gruperly/shared';
+import { getPaginationMetadata, getPaginationOffset } from '@/lib/pagination';
+import prisma from '@/lib/prisma';
+import { buildGroupWhereForUser, type GroupDb, toGroupDto } from '../../lib';
+
+type ListGroupsDeps = {
+  db?: Pick<GroupDb, 'group'>;
+};
+
+type GroupRecord = {
+  id: string;
+  name: string;
+  description: string | null;
+  createdById: string;
+  createdAt: Date;
+  updatedAt: Date;
+};
+
+export class ListGroups {
+  constructor(private readonly deps: ListGroupsDeps = {}) {}
+
+  async execute(
+    query: GroupQuery,
+    userId: string,
+  ): Promise<Result<GroupList, ProblemDetails>> {
+    const db = this.deps.db ?? prisma;
+    const where = buildGroupWhereForUser(userId) as Prisma.GroupWhereInput;
+
+    const [records, total] = await Promise.all([
+      db.group.findMany({
+        where,
+        skip: getPaginationOffset(query),
+        take: query.pageSize,
+        orderBy: { createdAt: 'desc' },
+      }),
+      db.group.count({ where }),
+    ]);
+
+    return ok({
+      data: records.map((record: GroupRecord) => toGroupDto(record)),
+      pagination: getPaginationMetadata(query, total),
+    });
+  }
+}