ci(admin-web): Docker build & push vers registry Gitea + reusable tests

- Nouveau Dockerfile multi-stage Next.js standalone (node:22-bookworm-slim)
- Configuration semantic-release (.releaserc.json, version.json, devDeps)
- docker-compose.portainer.yml pour déploiement Portainer
- Workflow docker-admin-web.yml : test → semantic-release → build push → deploy
- Extraction admin-web-tests.yml (reusable workflow) appelé par ci.yml et docker-admin-web.yml → 0 duplication
- next.config.ts : ajout output: 'standalone'
- .dockerignore : exclusions node_modules, .next, etc.

admin-web/.releaserc.json

@@ -0,0 +1,14 @@
+{
+  "branches": ["main"],
+  "plugins": [
+    "@semantic-release/commit-analyzer",
+    "@semantic-release/release-notes-generator",
+    ["@semantic-release/exec", {
+      "prepareCmd": "echo '{\"version\": \"${nextRelease.version}\"}' > version.json"
+    }],
+    ["@semantic-release/git", {
+      "assets": ["version.json"],
+      "message": "chore(release): ${nextRelease.version}\n\n${nextRelease.notes}"
+    }]
+  ]
+}