Apply release-audit fixes for the 0.1.0 release candidate

[mcdigman]

Mechanical fixes from the pre-release audit of PR #24. Merging this into dev updates the release-candidate PR automatically.

• License: relicensed from Apache-2.0 WITH LLVM-exception to plain Apache-2.0 (LICENSE text, pyproject SPDX expression, all SPDX headers, README); LICENSE copyright year bumped to 2026. Plain Apache-2.0 is also recognized by GitHub's license detection.
• SPDX headers added to pyakima/_version.py, docs/__init__.py, pyakima/demos/__init__.py, tests/__init__.py.
• Typo: Unsuported → Unsupported in error messages plus the matching test assertions.
• README / PyPI rendering: absolute raw.githubusercontent.com image URLs, GFM footnotes converted to a plain-numbered References section (PyPI resolves no relative URLs and does not render footnotes), benchmark file and LICENSE now hyperlinked.
• Docs: new Usage page pulls the README's Jitted Use and Spline Options sections into the Sphinx site via new doc:jitted/doc:options markers.
• Packaging: description is now "Fast, Numba-compatible Akima/makima spline interpolation for regular and irregular grids"; added Topic :: Software Development :: Libraries :: Python Modules classifier and a Changelog project URL; MANIFEST.in makes the sdist deliberately ship tests/, CHANGELOG.md, CITATION.cff.
• New files: CITATION.cff (with ORCID, feeds GitHub "Cite this repository" and Zenodo), starter CHANGELOG.md.
• Workflow hardening: all actions pinned to commit SHAs (version noted in comments), workflow-level permissions: contents: read everywhere, persist-credentials: false on every checkout.

Verification

• pytest: 183 passed (DTMCMC-dev env, numba 0.66/numpy 2.4.6)
• prek run --all-files: all hooks pass (including actionlint on the hardened workflows)
• sphinx -W docs build succeeds; Usage page and References render
• uv build + twine check: both distributions pass; sdist/wheel contents inspected (wheel ships _version.py, demos/, py.typed; sdist adds tests + metadata files)

🤖 Generated with Claude Code

[mcdigman]

Release-readiness review for PR #26, pinned to:

• base dev @ c37c6eb92aa3e42169290094d2aff7a6419e229c
• head release-audit-fixes @ ba2eb14d0b190b2220607d9fd625ac67e346463f

I reviewed the diff as a release-candidate readiness change set. I found no blocking issues and no evidence of unintended substantive code changes.

What I checked:

• Python/library behavior diff: limited to SPDX license header changes, added SPDX headers in previously missing files, and Unsuported -> Unsupported exception-string typo fixes plus matching assertions.
• Packaging metadata: generated wheel/sdist metadata has License-Expression: Apache-2.0, expected classifiers, keywords, project URLs, extras, and Markdown content type.
• Artifact contents: sdist includes CHANGELOG.md, CITATION.cff, LICENSE, source package, and tests; wheel remains package-only plus license/metadata.
• Workflow hardening: pinned action SHAs match the referenced tags, including the peeled commit for the annotated PyPI publish tag.
• README/docs surface: PyPI-facing absolute image URLs, numbered references, license link, benchmark link, and new docs usage include markers look consistent with the intended usability/findability changes.

Local verification:

• python -m pytest -> 183 passed
• NUMBA_DISABLE_JIT=1 python -m coverage run --branch --source=pyakima --omit='*/demos/*' -m pytest -> 183 passed
• python -m coverage report -m --fail-under=100 -> 100%
• python -m build --no-isolation -> sdist and wheel built successfully
• git diff --check c37c6eb92aa3e42169290094d2aff7a6419e229c...ba2eb14d0b190b2220607d9fd625ac67e346463f -> clean

Current PR checks are also green: build, coverage, floor, docs HTML, install floor/highest, mypy, prek, pydoclint, pylint, pyright, pytest, and skylos are passing. I could not run local twine check/readme_renderer or local Sphinx in this shell because those modules are not installed here, but the corresponding GitHub build and html jobs are passing on the pinned head.