Add admin routes to Fastify backend

Add Fastify admin route to Sofia backend with step-by-step guidance

Rapidly adding backend endpoints to Sofia without manual routing boilerplate

• · route endpoint path
• · handler function logic

• · Fastify route file in apps/api/src/routes/admin/

• · Fastify framework
• · Sofia backend structure

Sofia backend initialized; Fastify server running

• · route collision (suggest rename)
• · missing middleware (auto-inject)

• · step-by-step guidance
• · backend path convention
• · middleware auto-wiring