fix: wheel LICENSE should not reference examples-only MIT files

[andreahlert]

The wheel was shipping a LICENSE that mentioned MIT-licensed files from
examples/deep-researcher, but those files only exist in the source
distribution. Moved the third-party attribution to a dedicated
THIRD-PARTY-LICENSES file included only in the sdist.

Closes #641

Changes

• Stripped the MIT section from LICENSE (now pure Apache 2.0)
• Added THIRD-PARTY-LICENSES with the MIT attribution for deep-researcher
• Included THIRD-PARTY-LICENSES in sdist via pyproject.toml (not in license-files, so the wheel stays clean)

How I tested this

• Built wheel, confirmed LICENSE has no MIT section
• Built sdist, confirmed THIRD-PARTY-LICENSES is present
• test_release_config.py passing

Notes

Per ASF policy, LICENSE must reflect what's actually in the distribution.

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.

[andreahlert]

@skrawcz @elijahbenizzy ready for review.

[pjfanning]

This change is not correct.

We need to leave the source code LICENSE alone because the problem file with 3rd party license is in the source code.

What we need is a separate LICENSE file that gets added to the whl file during its build that omits the bit in source LICENSE about the file that we do not add to the whl.

[andreahlert]

@pjfanning Ah, let me see if I got this right now. The source tree LICENSE must keep the MIT attribution because examples/deep-researcher files are actually there. What needs to change is the wheel only, since it doesn't ship those examples and shouldn't carry the MIT notice.

I've reworked the approach: the source LICENSE is now untouched, and a separate LICENSE-wheel (Apache-only) is what Flit injects into the .whl via license-files. The sdist still gets the full LICENSE as before.

Can you take another look and see if this is what you had in mind?

[pjfanning]

lgtm