Add Gitea Actions CI/CD pipeline for automated testing and container builds

- Add .gitea/workflows/ci-cd.yaml with test and build-push jobs
- Tests run on every push to main, builds trigger on v* tags
- Builds both engine and UI Docker images to Gitea container registry
- Update Dockerfile to Python 3.12 (matches pyproject.toml requirement)
- Requires REGISTRY_USERNAME and REGISTRY_PASSWORD secrets in Gitea

Dockerfile

@@ -4,7 +4,7 @@
 # =============================================================================
 # BASE IMAGE
 # =============================================================================
-FROM python:3.11-slim AS base
+FROM python:3.12-slim AS base
 
 # System dependencies for TA-Lib and general build
 RUN apt-get update && apt-get install -y --no-install-recommends \