Clean LICENSE.txt to verbatim PSF-2.0; move CCP attribution to NOTICE.md

[ccpvertex]

Summary

• The previous `LICENSE.txt` was structurally PSF-2.0 but with "Python Software Foundation"/"PSF" → "CCP Games"/"CCP" and "Python" → "CARBON.IO" substituted throughout. The substitutions, while preserving the substance of the licence terms, mean downstream license-detection tools (GitHub's `licensee` gem, anything that matches against SPDX templates) can't classify the file. The repo currently shows "Other" in GitHub's sidebar and `licenseInfo.spdxId` comes back null on the API.
• This change follows the Apache pattern:
  • `LICENSE.txt` is now the verbatim SPDX PSF-2.0 template — Python/PSF references intact, canonical 2001-2006 copyright years kept (those are part of what tools match against, not a substantive claim).
  • New `NOTICE.md` carries the CCP attribution and makes explicit that CARBON.IO is a derivative work distributed by CCP Games on the same PSF-2.0 terms, with CCP Games as licensor in place of PSF and CARBON.IO as the licensed work in place of Python. No modification to the licence terms themselves.
  • `README.md` license section now points readers at `NOTICE.md` alongside `LICENSE.txt`.

What is and isn't changing

	Before	After
Grant of rights, retention requirement, derivative-work summary obligation, AS-IS, liability cap, termination, agency disclaimer, deemed acceptance	LICENSE.txt	LICENSE.txt + NOTICE.md (combined). Substance unchanged.
Named licensor / licensed-work in the operative text	CCP Games / CARBON.IO (modified)	PSF / Python (verbatim PSF-2.0), with NOTICE.md making explicit that CCP Games is licensor of CARBON.IO on the same terms
Machine-classifiability	Not detected — shows "Other"	Verbatim PSF-2.0 template (note: PSF-2.0 isn't yet in choosealicense.com's corpus, so GitHub's sidebar won't auto-detect it — but downstream SPDX-matching tools will, and any future addition of PSF-2.0 to that corpus will Just Work)

Legal has signed off on this approach (subject to the wording not materially changing and being clear to readers what licence is covering what bits).

Note on GitHub's sidebar

PSF-2.0 is not currently in choosealicense.com/_licenses, which is the corpus GitHub's `licensee` gem uses for detection. So even after this PR merges, the GitHub repo page will still show "Other" until choosealicense adds PSF-2.0. The clean LICENSE.txt is still worth having for SPDX-aware tooling, future detector improvements, and basic license hygiene.

Test plan

• Sanity check that the LICENSE.txt content matches https://spdx.org/licenses/PSF-2.0.html (verbatim).
• Read NOTICE.md and confirm the substantive licence terms remain unchanged from the previous LICENSE.txt.
• Confirm README.md license section reads clearly with the new file split.

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