Make the admin a member with a flag, and drop the second listener

The admin was a set of env credentials on its own loopback listener. That
bought network isolation, and charged a second port to tunnel and proxy and
a second credential in the password manager. It also sat outside the
SameSite protection the member cookie already had, and left every ban and
password reset with no actor to log.

is_admin on users reuses what was already there: the session, the login
rate limiter, ban-drops-sessions, CSRF. /admin is now a route on the member
mux. A member without the flag gets 404 rather than 403 — the pages are
none of their business, and "forbidden" confirms there is something to be
forbidden from.

Registration needs an invite and invites come from /admin, so an empty
database cannot grow its first user. seedAdmin breaks that circle exactly
once, from ADMIN_EMAIL and ADMIN_PASSWORD, and does nothing against a
database that already has users.

An admin cannot ban themselves: banning drops the target's sessions, and
nothing would be left that could undo it.

This reverses decision 8, which is rewritten rather than deleted, along
with the admin entry in the CONTEXT.md vocabulary.

main_test.go

@@ -7,29 +7,29 @@ import (
 	"testing"
 )
 
+// A plain member must not be able to tell that /admin exists, and a stranger must be sent to log in.
 func TestRequireAdmin(t *testing.T) {
-	a := &app{cfg: config{adminUser: "admin", adminPass: "s3cret"}}
-	h := a.requireAdmin(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	a := &app{}
+	h := a.requireAdmin(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusTeapot)
-	}))
+	})
 
 	for _, tc := range []struct {
-		name, user, pass string
-		auth             bool
-		want             int
+		name string
+		as   *member
+		want int
 	}{
-		{name: "no credentials", want: http.StatusUnauthorized},
-		{name: "wrong password", user: "admin", pass: "hunter2", auth: true, want: http.StatusUnauthorized},
-		{name: "wrong user", user: "root", pass: "s3cret", auth: true, want: http.StatusUnauthorized},
-		{name: "correct", user: "admin", pass: "s3cret", auth: true, want: http.StatusTeapot},
+		{name: "signed out", as: nil, want: http.StatusSeeOther},
+		{name: "member", as: &member{ID: 1}, want: http.StatusNotFound},
+		{name: "admin", as: &member{ID: 1, IsAdmin: true}, want: http.StatusTeapot},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			r := httptest.NewRequest("GET", "/admin", nil)
-			if tc.auth {
-				r.SetBasicAuth(tc.user, tc.pass)
+			if tc.as != nil {
+				r = r.WithContext(context.WithValue(r.Context(), memberKey, tc.as))
 			}
 			w := httptest.NewRecorder()
-			h.ServeHTTP(w, r)
+			h(w, r)
 			if w.Code != tc.want {
 				t.Fatalf("status = %d, want %d", w.Code, tc.want)
 			}
@@ -37,6 +37,43 @@ func TestRequireAdmin(t *testing.T) {
 	}
 }
 
+// The first account cannot arrive by invite, because minting an invite needs an admin.
+func TestSeedAdminOnlyOnEmptyDatabase(t *testing.T) {
+	a := testApp(t)
+	ctx := context.Background()
+	cfg := config{adminEmail: "[email protected]", adminName: "Ylläpito", adminPass: "salasana1"}
+
+	if err := seedAdmin(ctx, a.db, cfg); err != nil {
+		t.Fatal(err)
+	}
+	var name, email string
+	var isAdmin bool
+	if err := a.db.QueryRowContext(ctx,
+		`select name, email, is_admin from users`).Scan(&name, &email, &isAdmin); err != nil {
+		t.Fatal(err)
+	}
+	if !isAdmin || name != "Ylläpito" {
+		t.Fatalf("seeded %q is_admin=%v, want Ylläpito admin", name, isAdmin)
+	}
+	// Login is by lowercased email, so the seed must not smuggle in a capital.
+	if email != "[email protected]" {
+		t.Fatalf("email = %q, want lowercased", email)
+	}
+
+	// Re-running on a populated database must not add a second account or reset the first.
+	cfg.adminEmail = "[email protected]"
+	if err := seedAdmin(ctx, a.db, cfg); err != nil {
+		t.Fatal(err)
+	}
+	var n int
+	if err := a.db.QueryRowContext(ctx, `select count(*) from users`).Scan(&n); err != nil {
+		t.Fatal(err)
+	}
+	if n != 1 {
+		t.Fatalf("users = %d, want 1", n)
+	}
+}
+
 func TestMigrateIsIdempotent(t *testing.T) {
 	ctx := context.Background()
 	a := testApp(t) // already migrated once
@@ -52,7 +89,7 @@ func TestMigrateIsIdempotent(t *testing.T) {
 	if err := a.db.QueryRowContext(ctx, `select count(*) from schema_migrations`).Scan(&n); err != nil {
 		t.Fatal(err)
 	}
-	if n != 1 {
-		t.Fatalf("applied migrations = %d, want 1", n)
+	if n != 2 {
+		t.Fatalf("applied migrations = %d, want 2", n)
 	}
 }