Use the canonical Git mount for the public source clone link

The public source clone link is still assembled as https://reviewos.org/reviewos/reviewos.org.git in resources/functions/site.ts, even though the forge's supported HTTP Git mount is /git and the existing cloneUrl/cloneUrlFor helpers already encode it.

Observed after production deployed 08b9f75: a normal shallow clone of https://reviewos.org/git/reviewos/reviewos.org.git completed and passed git fsck --no-reflogs; the advertised unmounted URL returned “repository not found”. Neither command used a transport override or retry.

Use the canonical clone URL builder for SOURCE_CLONE_URL so public marketing and documentation copy the URL that works. Runner checkouts already use the canonical mount; this is separate from the web-memory/transfer issue in https://github.com/ReviewOS/reviewos.org/issues/8.

Fixed and normally deployed at https://github.com/ReviewOS/reviewos.org/commit/8b05734e8a8570df3e8fe3105131bb5442b89b9a through successful full CI: https://github.com/ReviewOS/reviewos.org/actions/runs/40919521264.

Live homepage responses contain the canonical https://reviewos.org/git/reviewos/reviewos.org.git link. Eight concurrent public homepage/docs/explore/repository requests returned 200. A fresh ordinary shallow clone through that mount resolved to 8b05734 and passed git fsck --no-reflogs, without transport overrides or retries.