Add OpenAI and PostgreSQL credential management

- Implemented OpenAICredencial class for managing OpenAI API keys.
- Created OpenAICredencialModel and OpenAICredencialMapper for SQLAlchemy integration.
- Developed OpenAICredencialRepo for CRUD operations on OpenAI credentials.
- Established OpenAICliente class for interacting with OpenAI API.
- Introduced PostgresCredencial class for managing PostgreSQL connection details.
- Created PostgresCredencialModel and PostgresCredencialMapper for SQLAlchemy integration.
- Developed PostgresCredencialRepo for CRUD operations on PostgreSQL credentials.
- Added base connection class and PostgreSQL connection implementation.
- Included environment variable loading for sensitive data management.

frontend/postcss.config.cjs

@@ -0,0 +1,14 @@
+module.exports = {
+  plugins: {
+    'postcss-preset-mantine': {},
+    'postcss-simple-vars': {
+      variables: {
+        'mantine-breakpoint-xs': '36em',
+        'mantine-breakpoint-sm': '48em',
+        'mantine-breakpoint-md': '62em',
+        'mantine-breakpoint-lg': '75em',
+        'mantine-breakpoint-xl': '88em',
+      },
+    },
+  },
+};