docs: list Python 3.14 in README badge

[MukundaKatta]

Summary

• replace the PyPI-supported-versions badge with an explicit README badge that includes Python 3.14
• align the displayed support range with pyproject classifiers and the CI matrix

Fixes #2537

Tests

• git diff --check

Note: no runtime tests were run; this is a README-only badge update.

[MukundaKatta]

Pushed 0cc6363 to fix the CI failure.

Root cause: README.md is frozen for v1 docs on main, and CI rejects changes there. I moved the Python 3.14 badge update into README.v2.md and restored README.md to the base version.

Validation run locally:

• SKIP=no-commit-to-branch,readme-v1-frozen uv run --with pre-commit pre-commit run --show-diff-on-failure --all-files --verbose
• git diff --check
• frozen README guard against origin/main