fix: Add Korean fonts to Docker image for PDF capture

- Add fonts-noto-cjk and fontconfig to backend Dockerfile
- Fixes garbled Korean text in performance check PDFs
- Update SERVER_INFRASTRUCTURE_PLAN.md with actual infrastructure

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

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

backend/Dockerfile

@@ -24,7 +24,11 @@ RUN apt-get update && apt-get install -y \
     libasound2 \
     libpango-1.0-0 \
     libcairo2 \
-    && rm -rf /var/lib/apt/lists/*
+    # Korean fonts for PDF capture
+    fonts-noto-cjk \
+    fontconfig \
+    && rm -rf /var/lib/apt/lists/* \
+    && fc-cache -fv
 
 # Install Python dependencies
 COPY requirements.txt .