Chore/add setup and contributing docs (#90)

* chore: add dev setup documentation

* Add agents.md files

* simplify contributing documentation

api/.env.example

@@ -5,14 +5,14 @@ LOG_LEVEL="DEBUG"
 # Change these values if you deploy the backend and frontend
 # on any hosting provider with some DNS. Please ensure to 
 # provide the URL with scheme like http or https
-# BACKEND_API_ENDPOINT: "http://localhost:8000"
-# UI_APP_URL: "http://localhost:3010"
+BACKEND_API_ENDPOINT="http://localhost:8000"
+UI_APP_URL="http://localhost:3000"
 
 # Database Configuration
 DATABASE_URL="postgresql+asyncpg://postgres:postgres@localhost:5432/postgres"
 REDIS_URL="redis://:redissecret@localhost:6379"
 
-# AWS S3 Configuration (required for SaaS mode)
+# AWS S3 Configuration
 ENABLE_AWS_S3="false"
 # AWS_ACCESS_KEY_ID=""
 # AWS_SECRET_ACCESS_KEY=""

api/AGENTS.md

@@ -0,0 +1,50 @@
+# API - Backend Service
+
+FastAPI backend for the Dograh voice AI platform.
+
+## Project Structure
+
+```
+api/
+├── app.py            # Application entry point, FastAPI setup
+├── routes/           # API endpoint handlers
+├── services/         # Business logic and integrations
+├── db/               # Database models and data access
+├── schemas/          # Pydantic request/response schemas
+├── tasks/            # Background jobs (ARQ)
+├── utils/            # Utility functions
+├── alembic/          # Database migrations
+├── constants.py      # Environment variables and constants
+└── tests/            # Test suite
+```
+
+## Where to Find Things
+
+| Looking for... | Go to... |
+|----------------|----------|
+| API endpoints | `routes/` - each file is a router module, aggregated in `routes/main.py` |
+| Business logic | `services/` - organized by domain (telephony, workflow, campaign, etc.) |
+| Database models | `db/models.py` |
+| Database queries | `db/*_client.py` files (repository pattern) |
+| Request/response types | `schemas/` |
+| Background tasks | `tasks/` - uses ARQ for async job processing |
+| Environment config | `constants.py` |
+
+## API Structure
+
+- All routes are mounted at `/api/v1` prefix
+- Routes are organized by domain (workflow, telephony, campaign, user, etc.)
+- `routes/main.py` aggregates all routers
+
+## Database Migrations
+
+```bash
+./scripts/makemigrate.sh "description"  # Create migration
+./scripts/migrate.sh                     # Run migrations
+```
+
+## Development
+
+```bash
+uvicorn api.app:app --reload --port 8000
+```

api/CLAUDE.md

@@ -0,0 +1 @@
+@AGENTS.md

api/routes/workflow.py

@@ -600,7 +600,7 @@ async def get_workflow_run(
             "call_duration_seconds": int(
                 round(run.cost_info.get("call_duration_seconds"))
             )
-            if run.cost_info
+            if run.cost_info and run.cost_info.get("call_duration_seconds") is not None
             else None,
         }
         if run.cost_info