feat(apigw): add API Gateway response streaming support (#207)

Replace ALB + Lambda architecture with API Gateway REST API + Lambda
using response streaming for SSE support. This provides:

- No VPC required, reducing complexity and cost
- Native streaming support via API Gateway response streaming
- Pay-per-request pricing model

Changes:
- Add Lambda Web Adapter to Dockerfile for streaming support
- Replace BedrockProxy.template with API Gateway configuration
- Update README with new deployment options and latest models
- Update architecture diagram for API Gateway flow

src/Dockerfile

@@ -1,9 +1,15 @@
 FROM public.ecr.aws/lambda/python:3.12
 
+# Add Lambda Web Adapter for API Gateway response streaming
+COPY --from=public.ecr.aws/awsguru/aws-lambda-adapter:0.9.1 /lambda-adapter /opt/extensions/lambda-adapter
+
 COPY ./api ./api
 
 COPY requirements.txt .
 
 RUN pip3 install -r requirements.txt -U --no-cache-dir
 
-CMD [ "api.app.handler" ]
+# Lambda Web Adapter requires overriding the Lambda base image entrypoint
+# to run the web app directly instead of the Lambda runtime handler
+ENTRYPOINT []
+CMD ["python", "-m", "uvicorn", "api.app:app", "--host", "0.0.0.0", "--port", "8080"]