chore: repoint remaining links at git.swaits.com

Rewrites lingering github.com / *.sr.ht references to this Gitea instance,
translating GitHub and Sourcehut URL shapes to Gitea's (/blob/<ref>/ and
sr.ht /tree/<ref>/item/ -> /src/branch/<ref>/, /tree/<tag> -> /src/tag/<tag>,
/actions/workflows/X -> /actions?workflow=X, /edit/ -> /_edit/).

Left pointing at the old hosts on purpose: pull-request links (PRs were not
migrated), forks that were never migrated, and GitHub-only surfaces Gitea
lacks. OpenPGP identity proofs are untouched by design.

versions/v0.1.0/07-payload-anon-req.md

@@ -66,7 +66,7 @@ Header payload type field: `0x07` (ANON_REQ)
 - [Section 6: Encrypted Payloads](06-payload-encrypted.md) — Standard encrypted format
 - [Section 14: Cryptography](14-crypto.md) — Encrypt-then-MAC
 - [Section 15: Identity](15-identity.md) — ECDH key exchange
-- Test vectors: [`corpus/payloads/anon-req/`](https://github.com/swaits/meshcore-spec/tree/main/versions/v0.1.0/corpus/payloads/anon-req/)
+- Test vectors: [`corpus/payloads/anon-req/`](https://git.swaits.com/swaits/meshcore-spec/src/branch/main/versions/v0.1.0/corpus/payloads/anon-req/)
 
 ### Reference Implementation