Add GitHub and Cloudflare to the default website check

[tcpiplab]

Adds github.com and www.cloudflare.com to DEFAULT_WEBSITES in
network_tools/web_check.py, taking that list from seventeen sites to nineteen.

Why these two

Both were already present in the fallback list inside network_diagnostics.py,
but not in the list the migrated web_check module actually uses. That fallback
only runs if importing the migrated module raises, so in practice neither site
was ever reached on a normal run.

They are also a different kind of canary from the ten consumer sites above them.
A developer notices GitHub being unreachable immediately, and Cloudflare fronts
a large share of the web, so Cloudflare failing while Google and Amazon still
answer is a useful signal in itself rather than just one more failure.

Verified

Both answer from this machine:

Reachable Websites (2):
  https://www.cloudflare.com: 0.087s
  https://github.com: 0.221s
Summary: Full Connectivity - All websites reachable

Note for the phonebot side

phonebot narrates this tool's output, and it now names the sites that failed
rather than only counting them. It does that from its own spoken-name table,
keyed on hostname, so that no text produced by this repository reaches a
text-to-speech engine. A test on that side reads this file directly and fails if
a site here has no spoken name, so the two repositories are checked against each
other rather than assumed to agree.

Both hostnames added here already have entries on that side, including the
www and bare variants, so nothing is needed beyond merging this.

🤖 Generated with Claude Code

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None