Fix Docker/CI: reproducible Windows build, Dockerfile cleanup

- Fix Windows CI build to use npm ci instead of deleting lockfile and
  running npm install, ensuring reproducible cross-platform builds
- Remove duplicate uv/ruff root installations from Dockerfile (only
  need the claude user installations)
- Make AWS CLI install architecture-aware using uname -m for arm64
  compatibility
- Remove unused SiblingContainers component (dead code)

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

.gitea/workflows/build-app.yml

@@ -192,8 +192,7 @@ jobs:
         run: |
           set "PATH=%USERPROFILE%\.cargo\bin;C:\Program Files\nodejs;%PATH%"
           if exist node_modules rmdir /s /q node_modules
-          if exist package-lock.json del package-lock.json
-          npm install
+          npm ci
 
       - name: Build frontend
         working-directory: ./app