feat(single-declaration): compute bölmə 3 income tax from payroll

Apply AZ progressive tax brackets (3%/10%/14%) per employee per month
on gross pay, then sum for monthly and quarterly tax amounts in
bölmə_3 hissə 1. Formula Editor stays responsible for the tax base
columns; this fills vergiməbləği* independently.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

taxes_az/taxes_az/doctype/single_declaration_related_to_salaried_and_non_salaried_work/single_declaration_related_to_salaried_and_non_salaried_work.js

@@ -91,6 +91,7 @@ function reload_hisse_1_data(frm) {
                 populate_child_table(frm, 'hissə_2', r.message.hisse_2_data || []);
                 populate_child_table(frm, 'hissə_3', r.message.hisse_3_data || []);
                 update_existing_rows(frm, 'bolme2_hisse1', r.message.bolme2_hisse1_data || {});
+                update_existing_rows(frm, 'bölmə_3', r.message.bolme_3_data || {});
                 populate_child_table(frm, 'vergi_', r.message.vergi_data || []);
                 populate_child_table(frm, 'mdss_', r.message.mdss_data || []);
                 populate_child_table(frm, 'issizlik', r.message.issizlik_data || []);

taxes_az/taxes_az/doctype/single_declaration_related_to_salaried_and_non_salaried_work/single_declaration_related_to_salaried_and_non_salaried_work.py

@@ -97,6 +97,7 @@ def populate_declaration_tables(company, year, quarter):
 		hisse_2_data = build_hisse_2(payroll)
 		hisse_3_data = get_absence_data(company, from_date, to_date)
 		bolme2_hisse1_data = get_bolme2_hisse1_data(company, year, quarter)
+		bolme_3_data = build_bolme_3(payroll, quarter)
 		elave4_data = build_elave4_tables(payroll)
 
 		return {
@@ -105,6 +106,7 @@ def populate_declaration_tables(company, year, quarter):
 			"hisse_2_data": hisse_2_data,
 			"hisse_3_data": hisse_3_data,
 			"bolme2_hisse1_data": bolme2_hisse1_data,
+			"bolme_3_data": bolme_3_data,
 			**elave4_data,
 		}
 
@@ -285,6 +287,52 @@ def build_elave4_tables(payroll):
 	return output
 
 
+def _calc_income_tax(gross):
+	# AZ progressive brackets: 3% / 75 + 10% over 2500 / 625 + 14% over 8000.
+	# Brackets are per-employee per-month — sum of per-employee taxes ≠ tax on summed base.
+	if gross <= 0:
+		return 0.0
+	if gross <= 2500:
+		return gross * 0.03
+	if gross <= 8000:
+		return 75 + (gross - 2500) * 0.10
+	return 625 + (gross - 8000) * 0.14
+
+
+def build_bolme_3(payroll, quarter):
+	"""Income tax (gəlir vergisi) per month, computed per-employee then summed."""
+	salary_slips = payroll["salary_slips"]
+	currency = payroll["currency"]
+	company_currency = payroll["company_currency"]
+
+	quarter_num = int(quarter[0])
+	start_month = (quarter_num - 1) * 3 + 1
+
+	per_emp_monthly_gross = {}
+	for ss in salary_slips:
+		month_index = ss.start_date.month - start_month + 1
+		if month_index not in (1, 2, 3):
+			continue
+		gp = flt(ss.gross_pay)
+		if currency == company_currency:
+			gp *= flt(ss.exchange_rate)
+		key = (ss.employee, month_index)
+		per_emp_monthly_gross[key] = per_emp_monthly_gross.get(key, 0.0) + gp
+
+	monthly_tax = {1: 0.0, 2: 0.0, 3: 0.0}
+	for (_emp, mi), gross in per_emp_monthly_gross.items():
+		monthly_tax[mi] += _calc_income_tax(gross)
+
+	return {
+		"Muzdlu işlə əlaqədar hesablamalar": {
+			"vergiməbləği": round(monthly_tax[1], 2),
+			"vergiməbləği2": round(monthly_tax[2], 2),
+			"vergiməbləği3": round(monthly_tax[3], 2),
+			"vergiməbləği4": round(monthly_tax[1] + monthly_tax[2] + monthly_tax[3], 2),
+		}
+	}
+
+
 def get_bolme2_hisse1_data(company, year, quarter):
 	"""Build data for bolme2_hisse1: employee counts per month of quarter."""
 	quarter_num = int(quarter[0])  # "1. Rüb" -> 1