feat(e-taxes-settings): auto-fill Default Item Group & UOM on install

The required Link fields default_item_group / default_uom had no field-level
default and nothing ever populated them, so every fresh base started with them
empty (had to be filled by hand). Add setup_defaults.ensure_settings_defaults()
that sets default_item_group="All Item Groups" and default_uom="Nos" — but only
when the field is blank AND the target record exists. Idempotent; wired into
after_install and after_migrate so it never overwrites an admin's choice.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

invoice_az/hooks.py

@@ -73,18 +73,22 @@ def after_install():
 	"""Run installation tasks"""
 	from invoice_az.auth import setup_token_renewal
 	from invoice_az.master_data.sync import sync_all
+	from invoice_az.setup_defaults import ensure_settings_defaults
 
 	setup_token_renewal()
 	sync_all()
+	ensure_settings_defaults()
 
 
 def after_migrate():
 	"""Run migration tasks"""
 	from invoice_az.auth import setup_token_renewal
 	from invoice_az.master_data.sync import sync_all
+	from invoice_az.setup_defaults import ensure_settings_defaults
 
 	setup_token_renewal()
 	sync_all()
+	ensure_settings_defaults()
 
 
 fixtures = []

invoice_az/setup_defaults.py

@@ -0,0 +1,33 @@
+import frappe
+
+# Sensible out-of-the-box defaults for E-Taxes Settings on a fresh base.
+# These are required Link fields with no field-level default, so without this
+# they start empty on every new install and have to be filled by hand.
+SETTINGS_DEFAULTS = {
+    "default_item_group": ("Item Group", "All Item Groups"),
+    "default_uom": ("UOM", "Nos"),
+}
+
+
+def ensure_settings_defaults():
+    """Populate E-Taxes Settings defaults if they are empty.
+
+    Idempotent: only writes a field when it is currently blank AND the target
+    record exists. Safe to run on every after_install / after_migrate — it
+    never overwrites a value an admin has already chosen.
+    """
+    settings = frappe.get_single("E-Taxes Settings")
+
+    changed = False
+    for fieldname, (doctype, value) in SETTINGS_DEFAULTS.items():
+        if settings.get(fieldname):
+            continue
+        if not frappe.db.exists(doctype, value):
+            continue
+        settings.set(fieldname, value)
+        changed = True
+
+    if changed:
+        settings.flags.ignore_permissions = True
+        settings.save(ignore_permissions=True)
+        frappe.db.commit()