feat: Phase 0 - Infrastructure and scaffolding (T-001 to T-003)

This commit establishes the foundational infrastructure for the Aegis
MITRE ATT&CK Coverage Platform.

T-001: Initialize project and Docker Compose
- Set up Docker Compose with PostgreSQL 15, MinIO, and FastAPI backend
- Create basic FastAPI application with health endpoint
- Configure persistent volumes for data storage

T-002: Configuration and database connection
- Add centralized configuration using pydantic-settings
- Implement SQLAlchemy database connection with session management
- Configure MinIO and JWT settings

T-003: Initialize Alembic for migrations
- Set up Alembic with PostgreSQL connection from settings
- Create initial empty migration
- Configure autogenerate support for future models

Also includes:
- Professional README with setup instructions
- Comprehensive .gitignore for Python/Node/Docker
- Project task plan (AegisTestPlan.md)

backend/app/config.py

@@ -0,0 +1,18 @@
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    DATABASE_URL: str = "postgresql://postgres:postgres@postgres:5432/attackdb"
+    SECRET_KEY: str = "change-me-in-production"
+    ALGORITHM: str = "HS256"
+    ACCESS_TOKEN_EXPIRE_MINUTES: int = 60
+    MINIO_ENDPOINT: str = "minio:9000"
+    MINIO_ACCESS_KEY: str = "minioadmin"
+    MINIO_SECRET_KEY: str = "minioadmin"
+    MINIO_BUCKET: str = "evidence"
+
+    class Config:
+        env_file = ".env"
+
+
+settings = Settings()