fix: Copy source files selectively to avoid overwriting lib directory

Instead of copying all files with 'COPY . .', copy specific directories
and files to avoid overwriting the built lib directory from the builder stage.

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

Co-Authored-By: Claude <[email protected]>

Author: marshallswain

Dockerfile.node12

@@ -40,8 +40,13 @@ COPY package*.json ./
 # Install dependencies
 RUN npm install --no-optional
 
-# Copy the rest of the application
-COPY . .
+# Copy package files and source files (but not lib directory)
+COPY --chown=node:node package*.json ./
+COPY --chown=node:node src ./src
+COPY --chown=node:node test ./test
+COPY --chown=node:node types ./types
+COPY --chown=node:node tsconfig.json ./
+COPY --chown=node:node .eslintrc.js ./
 
 # Copy built files from builder stage
 COPY --from=builder /app/lib ./lib