🐞🔧：make cross-document links absolute

[DerekNonGeneric]

Pull Request Purpose

This PR contains the following:

• 🐞🔧 bugfixing (🐜/🦟/🐛/🦗/🐝 et al.)
• 🆕🎏 implementation of new feature(s)
• ♻️ refactoring(s)
• 📄 documentation modification(s)
• 🔮 other

Testing

• yes (bugfixes and features will not be merged without tests)
• no

Link reference definitions in Markdown; no code path to cover. Every replacement URL was checked to return 200.

Breaking Changes

• yes (breaking changes will not be merged unless necessary)
• no

Description

These documents get read well outside this repository. GitHub surfaces them as the organization's community health files, and openinf.github.io imports five of them as pages under /docs. A repository-relative link only resolves in the first context — rendered at /docs/dev/faq/support/, ./CODE_OF_CONDUCT.md resolves against that URL and 404s.

Absolute URLs work in both places. README.md already writes its self-references as https://github.com/OpenINF/.github/blob/HEAD/…, so this follows the convention already in the repo rather than inventing one.

file	was	now
SUPPORT.md	./CODE_OF_CONDUCT.md	…/blob/HEAD/CODE_OF_CONDUCT.md
CONTRIBUTING.md	./CODE_OF_CONDUCT.md	…/blob/HEAD/CODE_OF_CONDUCT.md
CONTRIBUTING.md	./README.md	…/blob/HEAD/README.md
CONTRIBUTING.md	./SECURITY.md	…/blob/HEAD/SECURITY.md
CONTRIBUTING.md	./LICENSE.md	…/tree/HEAD/LICENSE

Note

That last row is a bug that predates this change and is broken in every context, including on GitHub. The prose in CONTRIBUTING.md says:

located within the [`LICENSE`][] folder in the root directory of the repository.

…but the only definition was [`LICENSE.md`]. The labels don't match, so the reference never resolved and the definition sat orphaned — and it pointed at ./LICENSE.md, when LICENSE is a directory holding MIT.txt, Apache-2.0.txt, and BlueOak-1.0.0.txt. The label now matches the prose and points at that directory. Happy to split this into its own PR if you'd rather keep this one to the relative→absolute change.

Why now

openinf.github.io validates its built pages with the W3C validator, and a fix there stops its import from rewriting your prose to make the links work. Keeping these links portable at the source means that site — and any other consumer — needs no such rewriting.

Follows #883.

List of any relevant issue numbers: none