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.

README.md

@@ -21,7 +21,7 @@ Zero config. ~12 lines of Lua.
 Add to your `vim.pack.add()` call:
 
 ```lua
-"https://github.com/swaits/tiny-checktime.nvim",
+"https://git.swaits.com/swaits/tiny-checktime.nvim",
 ```
 
 ## Configuration