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.

doc/tiny-packupdate.txt

@@ -31,7 +31,7 @@ changelogs, and an optional snacks.nvim picker for browsing results.
 
 Add to your |vim.pack.add()| call: >lua
 
-    "https://github.com/swaits/tiny-packupdate.nvim",
+    "https://git.swaits.com/swaits/tiny-packupdate.nvim",
 <
 Then in your config: >lua