Add ThunderPhone to closed-source projects

[kolchinski]

Adds ThunderPhone (https://thunderphone.com) — self-serve AI phone agent platform, launched publicly this week. Entry follows the existing format, placed alphabetically in the closed-source section.

[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: Alex Kolchinski.
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[cla-bot]

We require contributors to sign our Contributor License Agreement, and we don't have @kolchinski on file. You can sign our CLA at https://e2b.dev/docs/cla . Once you've signed, post a comment here that says '@cla-bot check'

[kolchinski]

@cla-bot check

[cla-bot]

The cla-bot has been summoned, and re-checked this pull request!