Randomise "free and open source" quote

[LuceCarter]

Instead of the current static text, update the "Free and open source" section to have randomised quotes about what Aspire is

[IEvangelist]

Triage → @Copilot

Scope: On the home page, the "Free and open source" section currently shows a single static line. Replace with a small randomised quote pool so each visit shows a different statement about what Aspire is.

Where

• Home page: src/frontend/src/content/docs/index.mdx (or the Astro component it pulls in — locate by grepping for the existing "Free and open source" string under src/frontend/).
• If a separate component file owns this region, edit it there and keep the page MDX clean.

Acceptance

• A small pool of 4–8 short, on-brand quotes lives in code (not MDX prose) and one is picked per render (server-side OK for static builds; client-side OK if it doesn't cause layout shift).
• The visual layout doesn't change — only the text content rotates.
• A11y unaffected — the quote is regular text, not a marquee/animation.
• No unrelated edits.

cc @LuceCarter (author) for quote-pool review.