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.

versions/v0.1.0/00-overview.md

@@ -23,7 +23,7 @@ The **upstream MeshCore C++ firmware is the source of truth** for all
 protocol behavior. This spec is downstream and derivative. Whenever the spec
 and the upstream C++ disagree, **upstream wins** — and a fix to this spec is
 filed against this repo, not against MeshCore. Each substantive change in
-[CHANGELOG.md](https://github.com/swaits/meshcore-spec/blob/main/CHANGELOG.md)
+[CHANGELOG.md](https://git.swaits.com/swaits/meshcore-spec/src/branch/main/CHANGELOG.md)
 records the upstream commit hash it was validated against.
 
 Refinements have also been driven in part by observations from building
@@ -31,10 +31,10 @@ DongLoRa firmware and apps against live MeshCore deployments. Where DongLoRa
 behavior diverges from upstream, this spec follows upstream and treats the
 DongLoRa side as a follow-up bug, not a spec change.
 
-Conformance against the [test corpus](https://github.com/swaits/meshcore-spec/tree/main/versions/v0.1.0/corpus)
+Conformance against the [test corpus](https://git.swaits.com/swaits/meshcore-spec/src/branch/main/versions/v0.1.0/corpus)
 is a useful signal but **not a substitute** for cross-checking against
 upstream firmware. If you find a divergence from upstream, please
-[file an issue](https://github.com/swaits/meshcore-spec/issues) — that is
+[file an issue](https://git.swaits.com/swaits/meshcore-spec/issues) — that is
 exactly the kind of report this project exists to catch.
 
 ### Spec Versions
@@ -61,7 +61,7 @@ version; switching keeps you on the same chapter where it exists in the
 target version. Spec versions use semver and are **independent** of the
 upstream MeshCore firmware's own versioning — each release records the
 upstream commit hash it was validated against in
-[CHANGELOG.md](https://github.com/swaits/meshcore-spec/blob/main/CHANGELOG.md).
+[CHANGELOG.md](https://git.swaits.com/swaits/meshcore-spec/src/branch/main/CHANGELOG.md).
 
 ### Scope