feat: Add PostgreSQL support and configuration setup for PunimTag

This commit introduces PostgreSQL as the default database for the PunimTag application, along with a new `.env.example` file for configuration. A setup script for PostgreSQL has been added to automate the installation and database creation process. The README has been updated to reflect these changes, including instructions for setting up PostgreSQL and using the `.env` file for configuration. Additionally, the database session management has been enhanced to support PostgreSQL connection pooling. Documentation has been updated accordingly.

src/web/db/session.py

@@ -1,10 +1,16 @@
 from __future__ import annotations
 
+from pathlib import Path
 from typing import Generator
 
+from dotenv import load_dotenv
 from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker
 
+# Load environment variables from .env file if it exists
+env_path = Path(__file__).parent.parent.parent.parent / ".env"
+load_dotenv(dotenv_path=env_path)
+
 
 def get_database_url() -> str:
     """Fetch database URL from environment or defaults."""
@@ -22,7 +28,22 @@ database_url = get_database_url()
 connect_args = {}
 if database_url.startswith("sqlite"):
     connect_args = {"check_same_thread": False}
-engine = create_engine(database_url, pool_pre_ping=True, future=True, connect_args=connect_args)
+
+# PostgreSQL connection pool settings
+pool_kwargs = {"pool_pre_ping": True}
+if database_url.startswith("postgresql"):
+    pool_kwargs.update({
+        "pool_size": 10,
+        "max_overflow": 20,
+        "pool_recycle": 3600,
+    })
+
+engine = create_engine(
+    database_url,
+    future=True,
+    connect_args=connect_args,
+    **pool_kwargs
+)
 SessionLocal = sessionmaker(bind=engine, autoflush=False, autocommit=False, future=True)