ci: build native Docker image and push to Gitea Container Registry

Adds:
- Dockerfile based on quarkus-micro-image:2.0 (~50MB base)
  Runs the native binary as non-root user 1001, exposes 8080
- .dockerignore to exclude build artifacts
- Gitea Actions workflow with 3 parallel jobs:
  - build-jvm: standard JAR (mvn package)
  - build-native: GraalVM native binary (mvn package -Pnative)
  - docker-native: takes the native binary artifact, builds
    the container image and pushes to
    gitea.danielarroyo.cl/proyectos/shot-crafter-calculator
    with tags 'latest' and short SHA

Triggers: push to main and PRs (docker job only on push).
Required secrets: GITEA_USERNAME, GITEA_TOKEN (write:packages).

.dockerignore

@@ -0,0 +1,8 @@
+.git
+target
+node_modules
+data
+.mvn
+*.md
+.gitignore
+.gitea