docs/ci: move workflow to .forgejo and add architecture diagram

backend/BACKEND.md

@@ -41,6 +41,30 @@ backend/
 └── docs/                   # Swagger documentation
 ```
 
+### 📊 Diagrama de Fluxo (C4 Simplificado)
+
+```mermaid
+graph TD
+    Client[📱 Clients (Frontend/App)] -->|JSON/HTTP| Router[🚦 Router (Mux)]
+    
+    subgraph "Core Backend"
+        Router --> Middleware[🛡️ Middleware (Auth, CORS)]
+        Middleware --> Handlers[🎮 HTTP Handlers]
+        
+        Handlers --> UseCases[🧠 Services & UseCases]
+        
+        UseCases --> Repos[💾 Repositories]
+        UseCases --> Adapters[🔌 External Adapters]
+    end
+    
+    Repos --> DB[(🐘 PostgreSQL)]
+    
+    Adapters --> Firebase[🔥 Firebase (FCM)]
+    Adapters --> LavinMQ[📨 LavinMQ]
+    Adapters --> Storage[☁️ S3/R2 Storage]
+    Adapters --> Stripe[💳 Stripe]
+```
+
 ---
 
 ## 🚀 Deployment & CI/CD (Forgejo)
@@ -48,7 +72,7 @@ backend/
 O deployment é automatizado via **Forgejo Actions**.
 
 ### Workflow: `Deploy Backend (Dev)`
-Arquivo: `.github/workflows/deploy.yaml`
+Arquivo: `.forgejo/workflows/deploy.yaml`
 
 Este workflow é disparado automaticamente ao realizar um push para o branch `dev` com alterações na pasta `backend/`.