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.

CHANGELOG.md

@@ -15,4 +15,4 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Configurable sign text and highlight group
 - Zero-config auto-loading via `plugin/` directory
 
-[0.1.0]: https://github.com/swaits/tiny-lightbulb.nvim/releases/tag/v0.1.0
+[0.1.0]: https://git.swaits.com/swaits/tiny-lightbulb.nvim/releases/tag/v0.1.0