chore: migrate from deprecated @anthropic-ai/claude-code to @anthropic-ai/claude-agent-sdk

Anthropic rebranded the SDK in 2025 from "Claude Code SDK" to "Claude Agent SDK". Updated all references across package.json, Dockerfile, and documentation to use the current @anthropic-ai/claude-agent-sdk package.

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

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

Dockerfile

@@ -97,7 +97,7 @@ COPY package*.json ./
 # Install Node.js dependencies as root
 RUN npm ci --only=production && \
     npm install -g zx && \
-    npm install -g @anthropic-ai/claude-code && \
+    npm install -g @anthropic-ai/claude-agent-sdk && \
     npm cache clean --force
 
 # Copy application code