feat: add full Zonemaster stack with Docker and Spanish UI

- Clone all 5 Zonemaster component repos (LDNS, Engine, CLI, Backend, GUI)
- Dockerfile.backend: 8-stage multi-stage build LDNS→Engine→CLI→Backend
- Dockerfile.gui: Astro static build served via nginx
- docker-compose.yml: backend (internal) + frontend (port 5353)
- nginx.conf: root redirects to /es/, /api/ proxied to backend
- zonemaster-gui/config.ts: defaultLanguage set to 'es' (Spanish)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

zonemaster/docs/internal/maintenance/ReleaseProcess-test-planning.md

@@ -0,0 +1,19 @@
+Release process - Test Planning
+===============================
+
+The purpose of test planning is to raise the quality by making the release
+testing more structured, getting better coverage and finding more bugs.
+This gives us greater faith in our releases.
+
+## Release testing start up-meeting
+
+1. Compile a list of all pull requests that should be tested.
+
+2. For each test item, discuss how it could and should be tested.
+   Make sure there is a heading titled "How to test this PR" in the pull request
+   description.
+   Add it if needed.
+   Add/update notes under this heading to reflect the conclusions made.
+
+3. Discuss prioritization of the test items and who should test what.
+   Note down all the conclusions.