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.

book.toml

@@ -8,8 +8,8 @@ src = "src"
 [output.html]
 default-theme = "navy"
 preferred-dark-theme = "navy"
-git-repository-url = "https://github.com/swaits/meshcore-spec"
-edit-url-template = "https://github.com/swaits/meshcore-spec/edit/main/{path}"
+git-repository-url = "https://git.swaits.com/swaits/meshcore-spec"
+edit-url-template = "https://git.swaits.com/swaits/meshcore-spec/_edit/main/{path}"
 # CI overrides per-version with MDBOOK_OUTPUT__HTML__SITE_URL.
 # Default below targets the "latest" deploy from main.
 site-url = "/meshcore-spec/latest/"