docs & cleanup: update stack info, remove dead code, fix backend bugs

- Fix AGENTS.md and 技术架构设计.md to reflect actual stack (Prisma+MySQL, static export, PM2)
- Remove 4 unused frontend components (page-transition, page-layout, image-upload, section-card)
- Fix card.tsx hardcoded colors → CSS variables
- Remove provider name from model selector, remove sensenova-u1-fast from models
- Fix analytics.controller.ts raw SQL table names (runtime bug)
- Add JWT auth guard to tools POST endpoint
- Fix AI gateway test: update env vars and model names
- Fix admin test: mock role structure for Prisma relation

backend/src/modules/admin/tests/admin.service.spec.ts

@@ -51,7 +51,7 @@ describe('AdminService', () => {
       id: 1,
       username: 'admin',
       passwordHash: '$2a$10$hashed',
-      role: 'superadmin',
+      role: { name: 'superadmin' },
       status: 'ACTIVE',
     };