docs: configure Sphinx directly and drop unmaintained sphinx-pyproject

[priya-sundaram-dev]

Describe your change:

Replaces #15123 as a clean PR touching only docs/conf.py and pyproject.toml (no changes to uv.lock), per @cclauss's request.

sphinx-pyproject has no release supporting Python 3.14/3.15 and pins an old Sphinx, which blocks the docs build on newer interpreters. This PR:

• Moves the [tool.sphinx-pyproject] table into a plain docs/conf.py. Project name/version/author are single-sourced from pyproject.toml via the stdlib tomllib, so they never drift from the packaging metadata.
• Drops the sphinx-pyproject dependency (main deps + docs group) and depends on sphinx>=8.2 directly.
• Bumps beautifulsoup4>=4.15 and pandas>=2.3.3.

docs/conf.py executes cleanly and ruff check/ruff format pass.

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. Comment: docs/build config only.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

[priya-sundaram-dev]

CI note: the docs-relevant checks are green — `build_docs` ✅, `ruff` ✅, `pre-commit.ci` ✅. The one red check (`build`) is an unrelated flake: `linear_algebra/matrix_inversion.py` doctest got scheduled onto a pytest-run-parallel worker (FAILED [thread-unsafe]: pytest-run-parallel does not support doctests), which is nondeterministic and independent of this PR (it only touches docs/conf.py + pyproject.toml). A re-run of build should clear it.