feat(01-01): create FastAPI application structure with health endpoint

- Add FastAPI app with title 'Debate API' v1.0.0
- Configure pydantic-settings for environment-based configuration
- Create /health endpoint at root level
- Create /api/v1/health and /api/v1/health/ready endpoints
- Disable docs/redoc in production environment

backend/__init__.py

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+# Debate Backend Package

backend/app/__init__.py

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+# Debate Backend Application

backend/app/api/__init__.py

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+# API package

backend/app/api/v1/__init__.py

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+# API v1 package

backend/app/api/v1/endpoints/__init__.py

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+# API v1 endpoints package

backend/app/api/v1/endpoints/health.py

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+"""Health check endpoints."""
+
+from fastapi import APIRouter
+
+router = APIRouter()
+
+
+@router.get("")
+async def health_check() -> dict[str, str]:
+    """Basic health check endpoint."""
+    return {"status": "healthy"}
+
+
+@router.get("/ready")
+async def readiness_check() -> dict[str, str]:
+    """Readiness check endpoint (DB check added in plan 01-02)."""
+    return {"status": "ready"}

backend/app/api/v1/router.py

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+"""API v1 router configuration."""
+
+from fastapi import APIRouter
+
+from backend.app.api.v1.endpoints import health
+
+api_router = APIRouter()
+
+api_router.include_router(health.router, prefix="/health", tags=["health"])

backend/app/core/__init__.py

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+# Core application components

backend/app/core/config.py

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+"""Application configuration via pydantic-settings."""
+
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    """Application settings loaded from environment variables."""
+
+    # Database
+    database_url: str = "postgresql+asyncpg://debate:debate_dev@localhost:5433/debate"
+
+    # Security
+    secret_key: str = "change-me-in-production"
+    csrf_secret_key: str = "change-me-in-production"
+
+    # Environment
+    environment: str = "development"
+    debug: bool = True
+
+    # CORS and trusted hosts
+    allowed_hosts: str = "localhost,127.0.0.1"
+    allowed_origins: str = "http://localhost:3000,http://127.0.0.1:3000"
+
+    # Cookie settings
+    cookie_domain: str = "localhost"
+
+    @property
+    def allowed_hosts_list(self) -> list[str]:
+        """Parse allowed hosts as a list."""
+        return [h.strip() for h in self.allowed_hosts.split(",") if h.strip()]
+
+    @property
+    def allowed_origins_list(self) -> list[str]:
+        """Parse allowed origins as a list."""
+        return [o.strip() for o in self.allowed_origins.split(",") if o.strip()]
+
+    @property
+    def is_production(self) -> bool:
+        """Check if running in production environment."""
+        return self.environment == "production"
+
+    class Config:
+        """Pydantic settings configuration."""
+
+        env_file = ".env"
+        env_file_encoding = "utf-8"
+        extra = "ignore"
+
+
+# Global settings instance
+settings = Settings()

backend/app/main.py

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+"""FastAPI application entry point."""
+
+from fastapi import FastAPI
+
+from backend.app.api.v1.router import api_router
+from backend.app.core.config import settings
+
+app = FastAPI(
+    title="Debate API",
+    version="1.0.0",
+    description="Backend API for Debate - Linux distribution customization platform",
+    docs_url="/docs" if not settings.is_production else None,
+    redoc_url="/redoc" if not settings.is_production else None,
+    debug=settings.debug,
+)
+
+# Include API routers
+app.include_router(api_router, prefix="/api/v1")
+
+
+@app.get("/health")
+async def root_health() -> dict[str, str]:
+    """Root health check endpoint."""
+    return {"status": "healthy"}