feat(demo): uncomment feature demos and add fake-useragent dependency

Uncomments demonstration code for memory dispatcher, streaming support,
content scraping, JSON schema generation, LLM markdown, and robots compliance
in the v0.4.3b2 features demo file. Also adds fake-useragent package as a
project dependency.

This change makes all feature demonstrations active by default and ensures
proper user agent handling capabilities.

pyproject.toml

@@ -37,6 +37,7 @@ dependencies = [
     "rich>=13.9.4",
     "cssselect>=1.2.0",
     "httpx==0.27.2",
+    "fake-useragent>=2.0.3"
 ]
 classifiers = [
     "Development Status :: 4 - Beta",