Messages: Add archive (soft-delete) support + dropdown UI polish

- Implemented `/account/messages/archive` route for soft-archiving messages
- Added `is_archived` flag to `users_messages` schema and model
- Topbar dropdown now reflects accurate unread message count
- Fixed missing route registration for archive handler
- Improved message visibility checks to prevent access violations
- Placeholder for rate-limit (429) error page rendering identified

handlers/messages.go

@@ -52,3 +52,23 @@ func ReadMessageHandler(db *sql.DB) http.HandlerFunc {
 		tmpl.ExecuteTemplate(w, "layout", context)
 	}
 }
+
+func ArchiveMessageHandler(db *sql.DB) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		id := helpers.Atoi(r.URL.Query().Get("id"))
+		userID, ok := helpers.GetCurrentUserID(r)
+		if !ok {
+			helpers.RenderError(w, r, 403)
+			return
+		}
+
+		err := storage.ArchiveMessage(db, userID, id)
+		if err != nil {
+			helpers.SetFlash(w, r, "Failed to archive message.")
+		} else {
+			helpers.SetFlash(w, r, "Message archived.")
+		}
+
+		http.Redirect(w, r, "/account/messages", http.StatusSeeOther)
+	}
+}