feat(server): add auth, user, and studio modules

Auth: WeChat login, JWT, roles guard (24 tests passing)
User: profile CRUD, training stats with month/total calculations
Studio: config management with auto-default creation

packages/server/src/studio/studio.service.ts

@@ -0,0 +1,34 @@
+import { Injectable } from '@nestjs/common'
+import { StudioConfig } from '@prisma/client'
+import { PrismaService } from '../prisma/prisma.service'
+import { UpdateStudioDto } from './dto/update-studio.dto'
+
+@Injectable()
+export class StudioService {
+  constructor(private readonly prisma: PrismaService) {}
+
+  async getInfo(): Promise<StudioConfig> {
+    const existing = await this.prisma.studioConfig.findFirst()
+
+    if (existing) {
+      return existing
+    }
+
+    return this.prisma.studioConfig.create({
+      data: {
+        name: '普拉提工作室',
+      },
+    })
+  }
+
+  async updateInfo(dto: UpdateStudioDto): Promise<StudioConfig> {
+    const existing = await this.getInfo()
+
+    const updated = await this.prisma.studioConfig.update({
+      where: { id: existing.id },
+      data: { ...dto },
+    })
+
+    return { ...updated }
+  }
+}