Optimize build: Kaniko cache flags, split Dockerfile stages, install-tools script

- Kaniko: --cache-ttl=168h, --snapshot-mode=redo, --compressed-caching=false
- Dockerfile: Split server-build into server-deps + server-build for better layer caching
- Replace rm+reinstall node_modules with npm prune --omit=dev
- Move ffmpeg/yt-dlp install to tools/install-tools.sh (single RUN layer)
- Remove separate ffmpeg-fetch stage and inline curl/yt-dlp install
- Remove $CI_COMMIT_SHA tag destination (unused, saves push time)
- bump-version: alpine/git image instead of alpine + apk add git

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

.gitlab-ci.yml

@@ -47,13 +47,12 @@ docker-build:
         CHANNEL="dev"
       fi
 
-      DESTINATIONS="--destination=$IMAGE_NAME:$CI_COMMIT_SHA --destination=$IMAGE_NAME:$TAG"
+      DESTINATIONS="--destination=$IMAGE_NAME:$TAG"
       if [ "$CI_COMMIT_REF_NAME" = "main" ]; then
         DESTINATIONS="$DESTINATIONS --destination=$IMAGE_NAME:latest"
       fi
 
       echo "Building for channel $CHANNEL with version $VERSION and tag $TAG"
-      echo "Using registry image: $IMAGE_NAME"
 
       /kaniko/executor \
         --context "$CI_PROJECT_DIR" \
@@ -62,6 +61,9 @@ docker-build:
         --build-arg "VITE_APP_VERSION=$VERSION" \
         --cache=true \
         --cache-repo="$IMAGE_NAME/cache" \
+        --cache-ttl=168h \
+        --snapshot-mode=redo \
+        --compressed-caching=false \
         --insecure-registry=$INTERNAL_REGISTRY \
         $DESTINATIONS
 
@@ -106,12 +108,11 @@ deploy:
 
 bump-version:
   stage: bump-version
-  image: alpine:latest
+  image: alpine/git:latest
   needs: [deploy]
   rules:
     - if: $CI_COMMIT_BRANCH == "main" && $CI_COMMIT_TITLE !~ /\[skip ci\]/
   script:
-    - apk add --no-cache git
     - |
       git config user.name "GitLab CI"
       git config user.email "ci@adriahub.de"