ci: publish-on-release workflow + maven-publish (caffeine)

- .gitea/workflows/build.yml: on release -> subochev/devops/publish -> caffeine
- maven-publish wired into api/client/server (KMP per-target publications)
- root: caffeine repo (nexus.xx) + pom; version via gradle.properties, overridable by -Pversion

.gitea/workflows/build.yml

@@ -0,0 +1,15 @@
+name: 'Publish AG-UI Protocol'
+on:
+  release:
+    types: [published]
+jobs:
+  deploy-dev:
+    name: 'Deploy to dev'
+    runs-on: ubuntu-latest
+    steps:
+      - name: 'Checkout'
+        uses: https://github.com/actions/checkout@v4
+      - name: 'Publishing Gradle'
+        uses: https://git.binom.pw/subochev/devops/publish@main
+        with:
+          version: ${{ gitea.ref_name }}