Add replace-build-vars composite action, wire into docker.yaml

Replaces {{BUILD_VAR_*}} placeholders in all text files of the calling
repo's checkout with Gitea Actions build/commit/branch info before the
docker build step runs. Language-agnostic (plain text substitution),
runs unconditionally, no-op when no placeholders are present.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01VVTCJvvJmS4fCSrm5wxwVo

.gitea/workflows/docker.yaml

@@ -43,6 +43,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Replace build placeholders
+        uses: UltimateCoder/resuable-workflows/actions/replace-build-vars@v3
+
       - name: Build Image
         run: |
           docker build \

actions/replace-build-vars/action.yml

@@ -0,0 +1,42 @@
+name: Replace Build Placeholders
+description: >
+  Ersetzt {{BUILD_VAR_*}}-Platzhalter in allen Textdateien durch Gitea-Actions-Build-Infos
+  (Commit, Branch, Run-Metadaten, …). Sprachunabhängig (reiner Text-Replace,
+  kein Build-Tool-Bezug), kein Input nötig.
+runs:
+  using: composite
+  steps:
+    - shell: bash
+      run: |
+        set -euo pipefail
+
+        SHA_SHORT="${GITHUB_SHA:0:7}"
+        BUILD_DATE="$(date -u '+%Y-%m-%dT%H:%M:%SZ')"
+
+        declare -A VARS=(
+          [BUILD_VAR_GITHUB_SHA]="${GITHUB_SHA:-}"
+          [BUILD_VAR_GITHUB_REF_NAME]="${GITHUB_REF_NAME:-}"
+          [BUILD_VAR_GITHUB_REF_TYPE]="${GITHUB_REF_TYPE:-}"
+          [BUILD_VAR_GITHUB_REPOSITORY]="${GITHUB_REPOSITORY:-}"
+          [BUILD_VAR_GITHUB_REPOSITORY_OWNER]="${GITHUB_REPOSITORY_OWNER:-}"
+          [BUILD_VAR_GITHUB_RUN_ID]="${GITHUB_RUN_ID:-}"
+          [BUILD_VAR_GITHUB_RUN_NUMBER]="${GITHUB_RUN_NUMBER:-}"
+          [BUILD_VAR_GITHUB_RUN_ATTEMPT]="${GITHUB_RUN_ATTEMPT:-}"
+          [BUILD_VAR_GITHUB_RETENTION_DAYS]="${GITHUB_RETENTION_DAYS:-}"
+          [BUILD_VAR_GITHUB_SERVER_URL]="${GITHUB_SERVER_URL:-}"
+          [BUILD_VAR_GITHUB_EVENT_NAME]="${GITHUB_EVENT_NAME:-}"
+          [BUILD_VAR_GITHUB_BASE_REF]="${GITHUB_BASE_REF:-}"
+          [BUILD_VAR_GITHUB_HEAD_REF]="${GITHUB_HEAD_REF:-}"
+          [BUILD_VAR_GITHUB_ACTION_REF]="${GITHUB_ACTION_REF:-}"
+          [BUILD_VAR_GITHUB_ACTION_REPOSITORY]="${GITHUB_ACTION_REPOSITORY:-}"
+          [BUILD_VAR_GITEA_ACTIONS_RUNNER_VERSION]="${GITEA_ACTIONS_RUNNER_VERSION:-}"
+          [BUILD_VAR_COMMIT_SHA_SHORT]="$SHA_SHORT"
+          [BUILD_VAR_BUILD_DATE]="$BUILD_DATE"
+        )
+
+        SED_ARGS=()
+        for key in "${!VARS[@]}"; do
+          SED_ARGS+=(-e "s|{{${key}}}|${VARS[$key]}|g")
+        done
+
+        grep -rIl --exclude-dir=.git '' . | xargs -r sed -i "${SED_ARGS[@]}"