feat: add pre-baked CI build images

- cameleer-build:1 — Maven 3.9 + Java 17 + Node.js 22 + curl/jq/procps/bc
- cameleer-docker-builder:1 — Docker 27 + git/curl/jq

Eliminates per-build tool installation across cameleer3 and cameleer3-server.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitattributes

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+* text=auto eol=lf

.gitea/workflows/ci.yml

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+name: Build Images
+
+on:
+  push:
+    branches: [main]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container:
+      image: docker:27
+    steps:
+      - run: apk add --no-cache git
+
+      - run: git clone --depth=1 https://cameleer:${REGISTRY_TOKEN}@gitea.siegeln.net/${GITHUB_REPOSITORY}.git .
+        env:
+          REGISTRY_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+
+      - run: echo "$REGISTRY_TOKEN" | docker login gitea.siegeln.net -u cameleer --password-stdin
+        env:
+          REGISTRY_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+
+      - name: Build and push build image
+        run: |
+          docker build -t gitea.siegeln.net/cameleer/cameleer-build:1 build/
+          docker push gitea.siegeln.net/cameleer/cameleer-build:1
+
+      - name: Build and push docker-builder image
+        run: |
+          docker build -t gitea.siegeln.net/cameleer/cameleer-docker-builder:1 docker-builder/
+          docker push gitea.siegeln.net/cameleer/cameleer-docker-builder:1

build/Dockerfile

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+FROM maven:3.9-eclipse-temurin-17
+
+# Node.js 22 LTS via NodeSource
+RUN apt-get update && apt-get install -y ca-certificates curl gnupg \
+    && mkdir -p /etc/apt/keyrings \
+    && curl -fsSL https://deb.nodesource.com/gpgkey/nodesource-repo.gpg.key \
+       | gpg --dearmor -o /etc/apt/keyrings/nodesource.gpg \
+    && echo "deb [signed-by=/etc/apt/keyrings/nodesource.gpg] https://deb.nodesource.com/node_22.x nodistro main" \
+       > /etc/apt/sources.list.d/nodesource.list \
+    && apt-get update && apt-get install -y nodejs procps bc jq \
+    && rm -rf /var/lib/apt/lists/*

docker-builder/Dockerfile

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+FROM docker:27
+
+RUN apk add --no-cache git curl jq