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/secret.yaml

@@ -0,0 +1,11 @@
+apiVersion: v1
+kind: Secret
+metadata:
+  name: invest-api-secrets
+  namespace: invest-api
+type: Opaque
+stringData:
+  # Replace with your actual keys before applying, or use sealed-secrets / external-secrets
+  INVEST_API_FINNHUB_API_KEY: ""
+  INVEST_API_FRED_API_KEY: ""
+  INVEST_API_ALPHAVANTAGE_API_KEY: ""