fix: pin fasthtml streaming examples

[JamBalaya56562]

Description

python-fasthtml==0.5.1 fails to import on python:3.12-slim with ModuleNotFoundError: sqlite_minutils, which broke both response-streaming examples at runtime. Because these examples use a Lambda Function URL with RESPONSE_STREAM and have no API Gateway events, sam local start-api (used by the existing test-image / test-zip jobs) cannot drive them — so they were only lint-validated and the broken pin shipped undetected.

This PR pins the examples to working versions and adds CI coverage that actually builds and runs them.

Changes

• Bump python-fasthtml to 0.13.4 in both fasthtml-response-streaming and fasthtml-response-streaming-zip examples.
• Bump anthropic to 0.40.0 in the image example. fasthtml 0.13.4 pulls httpx>=0.28, which dropped the proxies kwarg that anthropic 0.34.1 still passes, causing a TypeError at client construction.
• Add a test-stream CI job to .github/workflows/examples.yaml that builds and runs each streaming app, then verifies it responds over HTTP:
  • Image example: builds the app image (which COPYs the locally built adapter image) and runs it, mapping the container's 8080 to host 8000. AWS_REGION is set so AnthropicBedrock() can construct without real credentials; GET / only renders a form and never calls Bedrock.
  • Zip example: installs requirements.txt and runs app/main.py directly (the layer paths added by run.sh are only needed at runtime on Lambda).
  • The verify step polls / for up to 90s and asserts a non-5xx HTTP status, dumping app/container logs on failure.

Testing

• test-stream runs both examples in a matrix (fail-fast: false) and confirms each app starts and serves a valid response.

Why this matters

Without an end-to-end run, the broken python-fasthtml pin passed lint validation and shipped. This job closes that gap for the RESPONSE_STREAM examples that sam local start-api cannot exercise.