perf: optimize Vite build configuration for faster Docker builds (#403)

Major optimizations to resolve Docker build hanging at "rendering chunks..." phase:

**Vite Configuration (vite.config.ts)**:
- Switch minifier from terser to esbuild (10-100x faster)
- Disable sourcemap generation to reduce build time
- Implement aggressive chunk splitting for large dependencies:
  - monaco-editor (73MB) → separate chunk
  - mermaid (75MB) → separate chunk
  - @xterm (6.1MB) → separate chunk
  - vue-vendor, ui-vendor, vendor → logical groupings
- Enable CSS code splitting for better caching
- Increase chunk size warning limit to 1000KB
- Pre-bundle large dependencies (monaco-editor, mermaid, vue, pinia, naive-ui)

**Dockerfile Changes**:
- Add NODE_OPTIONS=--max-old-space-size=4096 to prevent OOM during build
- Move NODE_ENV=production before build step for consistency

**Root Cause Analysis**:
The build bottleneck was caused by three massive dependencies totaling ~150MB:
- monaco-editor (73MB) - VS Code editor for file editing
- mermaid (75MB) - Diagram rendering in chat messages
- @xterm (6.1MB) - Web terminal

These packages caused vite:asset (43%) and vite:terser (8%) phases to take
excessive time, especially in resource-constrained Docker environments.

**Expected Impact**:
- 50-70% faster build times (primarily from esbuild + pre-bundling)
- Eliminate hanging at "rendering chunks..." phase
- Better memory management during Docker builds

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -22,6 +22,8 @@ RUN ARCH=$(dpkg --print-architecture) \
 WORKDIR /app
 
 COPY package*.json ./
+# Increase Node.js memory limit to prevent OOM during build
+ENV NODE_OPTIONS=--max-old-space-size=4096
 RUN npm install --ignore-scripts && npm rebuild node-pty
 
 COPY . .