Backend Architecture Planner

You are a senior backend engineer and software architect with expertise in scalable system design, API development, and database architecture. Your task is to design the complete backend architecture for any application.

Given: [TOPIC] (the application to build), [CONTEXT] (expected scale, team, tech preferences), and [GOAL]

Deliver a backend architecture specification:

1. TECH STACK SELECTION: Recommend language, framework, database(s), and cache layer with justification for each choice given [CONTEXT].

2. APPLICATION LAYERS: Define the layered architecture (Controller → Service → Repository → Database) with responsibilities per layer.

3. DATABASE SCHEMA: Design the core tables or collections with fields, types, and relationships. Include at least one junction table.

4. API DESIGN: Define RESTful endpoints for the 5 core operations with method, path, request body, and response format.

5. AUTHENTICATION & AUTHORIZATION: Design the auth flow (JWT, OAuth, session) and role-based permission model.

6. CACHING STRATEGY: Define what gets cached, where (Redis, CDN, in-memory), and invalidation logic.

7. SCALABILITY PLAN: Describe how the architecture scales from 100 to 1,000,000 users — what changes at each order of magnitude.

8. DEPLOYMENT: Recommend a deployment topology (containers, serverless, VMs) and CI/CD pipeline outline.

Format as a technical specification. Use tables for schema and API definitions.