chore/docs: move to GitHub as the single home; drop archived-spec references

Codeberg is being retired as the project's public site, so every reference now
points at GitHub. That includes the Go module path (codeberg.org/mix/selfpost →
github.com/mixeme/selfpost): leaving an import path on a host that is going
away would break `go get` and `go install`, so this is not only a docs change.
Touches go.mod, test/e2e/go.mod, all imports, Makefile MODULE, the -ldflags
version stamp in build/Dockerfile and docs/development.md, the licence headers
in the SVG/HTML assets, and README (no more primary/mirror pair).

Comments no longer cite the archived specification. "spec 7.6.1", "spec 5.1"
and friends pointed into docs/archive/specification-v1.0.md, which is marked as
not a source of truth; each is now a reference to the live document that owns
the subject — architecture.md (with section), product.md, security.md or the
README. The review only asked for the 7.x refs (code-review.md § 4), but 4/5/6/
8/9 had the same defect, so they went too. Comments only, no behaviour change.

Also closes the remaining review items: architecture.md gained a Code layers
section with the layer diagram (A2), and TestParseDelivery gained the exotic
mail.log cases (§ 3).

Fixes a bug that last test found: the delivery-line pattern matched status=
greedily, taking the *last* occurrence on the line. Postfix appends the remote
server's reply verbatim, so a rejection whose reply quoted "status=sent" was
filed as a delivered message in the send log. It now takes the first status=
after the recipient, which is the real field.

R7 (CONTRIBUTING.md) moved to roadmap 2.x — one developer, no external PR flow,
so the file would have no audience yet. R1 (compose image tag) and the git tag
stay in roadmap § v1.x as the release-commit steps.

gofmt/go vet clean on both modules; go test ./... green except the three known
Windows-only failures (file perms, backslash paths, renaming an open file).
Not exercised on the dev server — no Docker locally.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/web/handlers_domains.go

@@ -6,12 +6,12 @@ import (
 	"net/http"
 	"strconv"
 
-	"codeberg.org/mix/selfpost/internal/store"
+	"github.com/mixeme/selfpost/internal/store"
 )
 
 // handleDashboard is the authenticated landing page: the list of sending
 // domains with their DKIM/selector and application counts, plus the add-domain
-// form (spec 7.2.2).
+// form (product.md).
 func (s *Server) handleDashboard(w http.ResponseWriter, r *http.Request) {
 	s.renderDashboard(w, r, http.StatusOK, "", "")
 }
@@ -48,7 +48,7 @@ func dashboardFlash(r *http.Request) string {
 
 // handleAddDomain validates the submitted name, creates the domain (DKIM key +
 // OpenDKIM reload), and redirects to the domain's page so the DNS record to
-// publish is shown (spec 7.2.3).
+// publish is shown (product.md).
 func (s *Server) handleAddDomain(w http.ResponseWriter, r *http.Request) {
 	if err := r.ParseForm(); err != nil {
 		s.renderDashboard(w, r, http.StatusBadRequest, "Invalid form submission.", "")
@@ -76,7 +76,7 @@ func (s *Server) handleAddDomain(w http.ResponseWriter, r *http.Request) {
 }
 
 // handleDeleteConfirm shows the cascade warning before a domain is removed: the
-// panel must explicitly state that all bound applications go with it (spec 7.2.4).
+// panel must explicitly state that all bound applications go with it (product.md).
 func (s *Server) handleDeleteConfirm(w http.ResponseWriter, r *http.Request) {
 	d, ok := s.lookupDomain(w, r)
 	if !ok {
@@ -116,11 +116,12 @@ func (s *Server) handleDeleteDomain(w http.ResponseWriter, r *http.Request) {
 }
 
 // handleReload re-applies both the OpenDKIM configuration and the Postfix
-// sender map on demand (spec 7.2.12). Each Resync regenerates its files from the
-// database and reloads its daemon, so the button doubles as a drift-recovery.
-// The button lives on the status page: it is a "put the daemons
-// back in the state the database describes" action, which belongs with the rest
-// of the server-health screen rather than in the domain list's top bar.
+// sender map on demand (architecture.md § Panel HTTP surface). Each Resync
+// regenerates its files from the database and reloads its daemon, so the
+// button doubles as a drift-recovery. The button lives on the status page: it
+// is a "put the daemons back in the state the database describes" action,
+// which belongs with the rest of the server-health screen rather than in the
+// domain list's top bar.
 func (s *Server) handleReload(w http.ResponseWriter, r *http.Request) {
 	if err := s.domains.Resync(); err != nil {
 		logf("panel: manual reload (opendkim): %v", err)