feat: add Docker, Drone CI, and k8s deployment manifests

- Dockerfile for Python 3.12 FastAPI app
- Drone CI pipeline to build and push to internal registry
- Kubernetes manifests (Deployment, Service, Secret, Namespace)
- ArgoCD Application for GitOps deployment
- Kustomize base configuration

k8s/base/kustomization.yaml

@@ -0,0 +1,10 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+namespace: invest-api
+
+resources:
+  - namespace.yaml
+  - secret.yaml
+  - deployment.yaml
+  - service.yaml