Fix: Add .dockerignore and optimize Dockerfile to reduce image size

The Space was stuck in BUILDING due to 194MB node_modules being included
in the Docker build context. Added .dockerignore and switched to selective
COPY for frontend source files.

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

.dockerignore

@@ -0,0 +1,11 @@
+node_modules
+.git
+.gitignore
+*.md
+backend/
+__pycache__
+*.pyc
+*.egg-info
+.env
+.venv
+.ruff_cache

Dockerfile

@@ -8,14 +8,16 @@ FROM node:20-slim AS frontend-builder
 
 WORKDIR /app/frontend
 
-# Copy package files
+# Copy package files first for layer caching
 COPY chatkit/frontend/package*.json ./
 
 # Install dependencies
 RUN npm ci --legacy-peer-deps
 
-# Copy source files
-COPY chatkit/frontend/ ./
+# Copy source files (after npm ci to leverage cache)
+COPY chatkit/frontend/src ./src
+COPY chatkit/frontend/public ./public
+COPY chatkit/frontend/index.html chatkit/frontend/vite.config.ts chatkit/frontend/tsconfig*.json chatkit/frontend/postcss.config.mjs chatkit/frontend/eslint.config.mjs ./
 
 # Build for production (output to dist/)
 RUN npm run build