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_monitor.go

@@ -6,12 +6,12 @@ import (
 	"net/http"
 	"strconv"
 
-	"codeberg.org/mix/selfpost/internal/logtail"
-	"codeberg.org/mix/selfpost/internal/postfix"
-	"codeberg.org/mix/selfpost/internal/store"
+	"github.com/mixeme/selfpost/internal/logtail"
+	"github.com/mixeme/selfpost/internal/postfix"
+	"github.com/mixeme/selfpost/internal/store"
 )
 
-// sendLogPageSize bounds each send-log page (spec 7.2's monitoring screens
+// sendLogPageSize bounds each send-log page (product.md's monitoring screens
 // call for pagination); logTailLines bounds how much of mail.log the log view
 // shows per refresh.
 const (
@@ -20,10 +20,10 @@ const (
 )
 
 // handleDeliveries renders the Deliveries page over the send log: server-side
-// filters by domain/application and pagination (spec 7.3.3). The row table
-// itself is the "deliveries_rows" fragment, shared verbatim with
-// handleDeliveriesRows so the initial page and its HTMX-polled refreshes never
-// diverge.
+// filters by domain/application and pagination (architecture.md §
+// Persistence). The row table itself is the "deliveries_rows" fragment, shared
+// verbatim with handleDeliveriesRows so the initial page and its HTMX-polled
+// refreshes never diverge.
 func (s *Server) handleDeliveries(w http.ResponseWriter, r *http.Request) {
 	data, err := s.sendLogData(r)
 	if err != nil {
@@ -38,7 +38,8 @@ func (s *Server) handleDeliveries(w http.ResponseWriter, r *http.Request) {
 }
 
 // handleDeliveriesRows serves the HTMX polling fragment for the delivery table
-// (spec 7.1: fragment endpoints return HTML, not JSON).
+// (architecture.md § Panel HTTP surface: fragment endpoints return HTML, not
+// JSON).
 func (s *Server) handleDeliveriesRows(w http.ResponseWriter, r *http.Request) {
 	data, err := s.sendLogData(r)
 	if err != nil {
@@ -110,7 +111,8 @@ func parsePage(v string) int {
 	return n
 }
 
-// handleMailQueue renders the Mail queue page (spec 7.2.11).
+// handleMailQueue renders the Mail queue page (architecture.md § Panel HTTP
+// surface).
 func (s *Server) handleMailQueue(w http.ResponseWriter, r *http.Request) {
 	out, errText := readQueue()
 	s.render(w, http.StatusOK, "mail_queue", map[string]any{
@@ -143,7 +145,8 @@ func readQueue() (string, string) {
 	return out, ""
 }
 
-// handleSystemLog renders the System log page over mail.log (spec 7.2.13).
+// handleSystemLog renders the System log page over mail.log (architecture.md §
+// Panel HTTP surface).
 func (s *Server) handleSystemLog(w http.ResponseWriter, r *http.Request) {
 	lines, errText := s.readLogTail()
 	s.render(w, http.StatusOK, "system_log", map[string]any{