🔧 chore(repo): restructure project file hierarchy

- move project files out of fleetledger directory to root
- update .gitignore to reflect new .env path

📝 docs(README): add detailed project description

- provide an overview of FleetLedger's features and usage
- include setup instructions and security notes

app/db.py

@@ -0,0 +1,21 @@
+from sqlmodel import SQLModel, create_engine, Session
+import os
+
+# SQLite database path, mapped to a Docker volume for persistence
+DB_PATH = os.getenv("DATABASE_PATH", "/data/fleetledger.db")
+
+engine = create_engine(
+    f"sqlite:///{DB_PATH}",
+    connect_args={"check_same_thread": False},
+)
+
+
+def init_db() -> None:
+    """Create all tables if they do not exist yet."""
+    SQLModel.metadata.create_all(engine)
+
+
+def get_session():
+    """FastAPI dependency that yields a SQLModel session."""
+    with Session(engine) as session:
+        yield session