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.

.build.yml

@@ -1,11 +0,0 @@
-image: alpine/edge
-secrets:
-  - 88cce185-d2ec-4573-9546-e33f36f79bbf
-sources:
-  - git+ssh://git@git.sr.ht/~swaits/thethethe.nvim
-tasks:
-  - mirror-to-github: |
-      cd ~/thethethe.nvim
-      ssh-keyscan -t rsa github.com >> ~/.ssh/known_hosts
-      git remote add github git@github.com:swaits/thethethe.nvim.git
-      git push --mirror github

README.md

@@ -17,7 +17,7 @@ in the background, so it doesn't delay startup time.
 
 ```lua
 {
-  "https://git.sr.ht/~swaits/thethethe.nvim",
+  "https://git.swaits.com/swaits/thethethe.nvim",
   lazy = true,
   event = "VeryLazy",
   opts = { },
@@ -28,7 +28,7 @@ in the background, so it doesn't delay startup time.
 
 ```lua
 {
-  "https://git.sr.ht/~swaits/thethethe.nvim",
+  "https://git.swaits.com/swaits/thethethe.nvim",
   config = function()
     require("thethethe").setup()
   end
@@ -38,7 +38,7 @@ in the background, so it doesn't delay startup time.
 ### [vim-plug](https://github.com/junegunn/vim-plug)
 
 ```vim
-Plug 'https://git.sr.ht/~swaits/thethethe.nvim'
+Plug 'https://git.swaits.com/swaits/thethethe.nvim'
 lua require("thethethe").setup()
 ```