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.

Cargo.toml

@@ -10,7 +10,7 @@ authors = ["Stephen Waits <steve@waits.net>"]
 license = "MIT"
 description = "Transparent LoRa radio over USB — plug in a board, talk LoRa from your host"
 repository = "https://git.swaits.com/donglora/firmware"
-homepage = "https://github.com/donglora/firmware"
+homepage = "https://git.swaits.com/donglora/firmware"
 keywords = ["lora", "radio", "embedded", "usb", "firmware"]
 categories = ["embedded", "hardware-support", "no-std"]