chore: repoint URLs at git.swaits.com and bump for release

Rewrites remaining github.com / git.sr.ht references to git.swaits.com,
translating GitHub URL shapes to Gitea's (/blob/<ref>/ -> /src/branch/<ref>/,
/tree/<tag> -> /src/tag/<tag>, /actions/workflows/X -> /actions?workflow=X,
/edit/ -> /_edit/).

Left pointing at GitHub on purpose: pull-request links (PRs were not migrated)
and GitHub-only surfaces Gitea lacks (security advisories, discussions).

Cargo.toml

@@ -1,13 +1,13 @@
 [package]
 name = "donglora-protocol"
-version = "1.1.0"
+version = "1.2.1"
 edition = "2024"
 rust-version = "1.85"
 authors = ["Stephen Waits <steve@waits.net>"]
 license = "MIT"
 description = "DongLoRa wire protocol types and COBS framing — shared between firmware and host crates"
 repository = "https://git.swaits.com/donglora/protocol-rs"
-homepage = "https://github.com/donglora/protocol-rs"
+homepage = "https://git.swaits.com/donglora/protocol-rs"
 documentation = "https://docs.rs/donglora-protocol"
 readme = "README.md"
 keywords = ["lora", "radio", "protocol", "no-std"]