fix: Fix Docker build for public directory

- Update Dockerfile to ensure public directory exists in builder stage
- Use 'COPY /app/public/. ./public/' pattern for robust copying
- Add manifest.json to public folder (non-empty directory)
- Remove .gitkeep placeholder

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Dockerfile

@@ -19,6 +19,9 @@ WORKDIR /app
 COPY --from=deps /app/node_modules ./node_modules
 COPY . .
 
+# Ensure public directory exists
+RUN mkdir -p public
+
 # Next.js telemetry
 ENV NEXT_TELEMETRY_DISABLED=1
 
@@ -34,7 +37,9 @@ ENV NEXT_TELEMETRY_DISABLED=1
 RUN addgroup --system --gid 1001 nodejs
 RUN adduser --system --uid 1001 nextjs
 
-COPY --from=builder /app/public ./public
+# Create public directory and copy contents if they exist
+RUN mkdir -p public
+COPY --from=builder /app/public/. ./public/
 
 # Set the correct permission for prerender cache
 RUN mkdir .next