Remove PostgreSQL and move to SQLite3

.env.example

@@ -0,0 +1,6 @@
+# Required backend secret. Use a long, random value in your local .env file.
+BACKEND_SECRET_KEY=please_change_me_to_a_long_random_string
+
+# Optional cookie settings for local/internal deployments.
+COOKIE_SECURE=false
+COOKIE_SAMESITE=Lax