refactor(settings): replace DATABASE_URL with explicit DB env vars

Replace the single `DATABASE_URL` connection string with individual
environment variables (`APP_DB_NAME`, `APP_DB_USER`, `APP_DB_PASSWORD`,
`DB_HOST`, `DB_PORT`) for more granular database configuration control.

mnemosyne/.env example

@@ -11,7 +11,11 @@ ALLOWED_HOSTS=localhost,127.0.0.1,mnemosyne.ouranos.helu.ca
 CSRF_TRUSTED_ORIGINS=http://localhost:8000,https://mnemosyne.ouranos.helu.ca
 
 # --- PostgreSQL Database ---
-DATABASE_URL=postgres://mnemosyne:password@portia.incus:5432/mnemosyne
+APP_DB_NAME=mnemosyne
+APP_DB_USER=mnemosyne
+APP_DB_PASSWORD=password
+DB_HOST=portia.incus
+DB_PORT=5432
 
 # --- Neo4j Graph Database ---
 NEOMODEL_NEO4J_BOLT_URL=bolt://neo4j:password@ariel.incus:25554

mnemosyne/mnemosyne/settings.py

@@ -98,10 +98,14 @@ WSGI_APPLICATION = "mnemosyne.wsgi.application"
 
 # --- Database: PostgreSQL (Django ORM) ---
 DATABASES = {
-    "default": env.db(
-        "DATABASE_URL",
-        default="postgres://mnemosyne:password@portia.incus:5432/mnemosyne",
-    ),
+    "default": {
+        "ENGINE": "django.db.backends.postgresql",
+        "NAME": env("APP_DB_NAME", default="mnemosyne"),
+        "USER": env("APP_DB_USER", default="mnemosyne"),
+        "PASSWORD": env("APP_DB_PASSWORD", default="password"),
+        "HOST": env("DB_HOST", default="portia.incus"),
+        "PORT": env("DB_PORT", default="5432"),
+    }
 }
 
 # --- Neo4j Graph Database ---