R-498: the app page's first steps name the household's address, not wiki.DOMAIN

AppInfo.WithAddress fills the catalog placeholder (<label>.DOMAIN -> the
effective subdomain + customer domain, bare DOMAIN -> the domain) on a
copy; appDetailHandler applies it. Pinned per catalog template (both
languages) and on the rendered page.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/stacks/appinfo_address.go

@@ -0,0 +1,51 @@
+package stacks
+
+import "regexp"
+
+// reDomainPlaceholder matches the catalog's address placeholder in app copy: a bare `DOMAIN` or a
+// `<label>.DOMAIN` (wiki.DOMAIN, https://paste.DOMAIN/…). `\b` keeps SUBDOMAIN and MAIL_DOMAIN out —
+// the letter or underscore before them is a word character, so no boundary falls inside them.
+var reDomainPlaceholder = regexp.MustCompile(`(?:([a-z0-9-]+)\.)?\bDOMAIN\b`)
+
+// WithAddress returns a copy of the app copy with the catalog's `DOMAIN` placeholder filled in
+// (R-498): `<label>.DOMAIN` becomes `<subdomain>.<domain>` — the app's EFFECTIVE subdomain (the one
+// the household chose at install), or the catalog label when none is known — and a bare `DOMAIN`
+// becomes `<domain>`. With no domain configured the copy is returned unchanged: a placeholder is
+// better than an address that is wrong. The receiver is not modified (slices are copied), because the
+// stack's metadata is shared with every other page. Pinned by TestR498_* (stacks and web).
+func (ai AppInfo) WithAddress(subdomain, domain string) AppInfo {
+	if domain == "" {
+		return ai
+	}
+	fill := func(s string) string {
+		return reDomainPlaceholder.ReplaceAllStringFunc(s, func(m string) string {
+			sub := reDomainPlaceholder.FindStringSubmatch(m)
+			if sub[1] == "" {
+				return domain
+			}
+			label := sub[1]
+			if subdomain != "" {
+				label = subdomain
+			}
+			return label + "." + domain
+		})
+	}
+	list := func(in []string) []string {
+		if in == nil {
+			return nil
+		}
+		out := make([]string, len(in))
+		for i, s := range in {
+			out[i] = fill(s)
+		}
+		return out
+	}
+	out := ai
+	out.Tagline = fill(ai.Tagline)
+	out.UseCases = list(ai.UseCases)
+	out.FirstSteps = list(ai.FirstSteps)
+	out.Prerequisites = list(ai.Prerequisites)
+	out.DefaultCreds = fill(ai.DefaultCreds)
+	out.AddPeople = fill(ai.AddPeople)
+	return out
+}