Chore: add donate call on the site

[scode2277]

What does this PR change?

Donation calls

Adds links to https://securityalliance.org/donate across the site and repo, with varied phrasing

Where	Copy
Top nav, beside the search bar	💜 Support us
Sidebar socials row	Heart icon, "Help sustain the Frameworks" on hover
Banner	"or chip in to keep this work going"
Version dropdown	Support the project
Contribute footer (end of every page)	💜 Keep this work funded, plus a supporting line
README.md, Contributing section	"Funding is another way to contribute."
contributing.mdx → CONTRIBUTING.md	Same, in the "Anything else?" section

Preview site -> https://chore-donate-buttons.frameworks-573.pages.dev

Type of change

• New content
• Edit to existing content
• Outline / structure change
• Typo or formatting fix
• Tooling / config

If applicable

• Editing existing content: tagged the current contributors from the attribution list
• Framework has a steward: asked them to review
• Outline change: updated vocs.config.ts with the dev: true parameter
• Want community feedback: shared this PR in our Discord

Stuck on anything? Just write it here and we're happy to help.