backend: add `vitest` tests for profile GET /me and PUT /me routes

[ShantKhatri]

Summary

Add tests for the existing authenticated profile endpoints in apps/backend/src/routes/profiles.ts.

Tasks

• create apps/backend/src/__tests__/profiles.test.ts.
• mock app.prisma to return a fake user for GET /api/profiles/me and assert displayName etc.
• mock app.prisma.user.update for PUT /api/profiles/me with valid input and assert body returned.
• confirm failure path for invalid accentColor returns 400 and has validation error details.

Acceptance Criteria

• asset test coverage for happy and invalid path.
• pnpm --filter @devcard/backend test passes.

[Dipti45sktech]

Hi @ShantKhatri , I would like to work on this issue, if you could assign it me?