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/setup.go

@@ -7,17 +7,17 @@ import (
 	"sync"
 	"time"
 
-	"codeberg.org/mix/selfpost/internal/store"
+	"github.com/mixeme/selfpost/internal/store"
 )
 
-// setupTokenTTL is the lifetime of a setup token (spec 7.6.1). After it
+// setupTokenTTL is the lifetime of a setup token (security.md). After it
 // elapses the token is regenerated and re-announced on the next /setup hit.
 const setupTokenTTL = 10 * time.Minute
 
 // setupManager owns the one-time administrator setup token. The token itself is
 // ephemeral (regenerated on restart or expiry) and lives only in memory; the
 // persistent "setup complete" fact is the presence of the admin row in the
-// store, so once that exists the token is gone for good (spec 7.6.1).
+// store, so once that exists the token is gone for good (security.md).
 type setupManager struct {
 	store     *store.Store
 	hostname  string
@@ -71,8 +71,8 @@ func (m *setupManager) activeToken() (string, bool) {
 
 // validate reports whether provided matches the active token, using a
 // constant-time comparison to avoid leaking a correct prefix via timing
-// (spec 7.6.1). A mismatch does NOT regenerate or invalidate the token: failed
-// attempts must not let an attacker DoS a legitimate setup (spec 7.6.1).
+// (security.md). A mismatch does NOT regenerate or invalidate the token: failed
+// attempts must not let an attacker DoS a legitimate setup (security.md).
 func (m *setupManager) validate(provided string) bool {
 	token, ok := m.activeToken()
 	if !ok {
@@ -94,13 +94,13 @@ func (m *setupManager) complete() {
 // regenerateLocked mints a fresh token, announces it and mirrors it to disk.
 // Caller holds m.mu.
 func (m *setupManager) regenerateLocked() {
-	m.token = randomToken(16) // 128 bits of entropy (spec 7.6.1)
+	m.token = randomToken(16) // 128 bits of entropy (security.md)
 	m.expiresAt = time.Now().Add(setupTokenTTL)
 	m.announce(m.token)
 }
 
 // announce prints the setup link to the container log and writes it to the
-// token file so it can be read either way (spec 7.6.1).
+// token file so it can be read either way (security.md).
 func (m *setupManager) announce(token string) {
 	url := m.setupURL(token)
 	logf("panel: ==================================================================")