fix: Docker build — restore .git and fix bundle permissions

- Remove .git/ from .dockerignore (needed for gemspec git ls-files)
- Fix /bundle permissions with chown for circleci user

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

Author: pftg

.dockerignore

@@ -2,7 +2,7 @@
 .ruby-lsp/
 coverage/
 tmp/
-.git/
+# Keep .git/ — needed for gemspec git ls-files and VCS checkout in tests
 .idea/
 .claude/
 .bundle/

Dockerfile

@@ -51,7 +51,7 @@ WORKDIR /app
 # Copy entire project (needed for git dependencies in gems.rb)
 COPY --chown=circleci:circleci . .
 
-# Install gems with cached bundle
-RUN --mount=type=cache,target=/bundle \
+# Install gems
+RUN sudo chown -R circleci:circleci /bundle && \
     bundle config set without 'tools' && \
     bundle install