frappix: add mysqlclient to insights for ibis mysql backend

insights' after_migrate hook connects to the Site DB data source via
ibis.mysql; the ibis 12 mysql backend imports MySQLdb, which frappix
does not ship. Fixes b4lerp migrate failing on bosona.

pkgs/frappix/overlay.nix

@@ -2,8 +2,15 @@
 # Must be applied after frappixFrappeOverlay (needs prev.frappix).
 final: prev: {
   frappix = prev.frappix.overrideScope (
-    ffinal: _fprev: {
+    ffinal: fprev: {
       default_thai_company = ffinal.callPackage ./default-thai-company.nix { };
+
+      # insights' after_migrate hook opens the "Site DB" data source via
+      # ibis.mysql, whose backend imports MySQLdb (mysqlclient) since ibis 10.
+      # Upstream frappix only ships ibis-framework without the mysql extra.
+      insights = fprev.insights.overridePythonAttrs (old: {
+        dependencies = old.dependencies ++ [ final.python3.pkgs.mysqlclient ];
+      });
     }
   );
 }