feat: Thai personal income tax exemption categories for HRMS

Fixtures for Employee Tax Exemption Category / Sub Category covering the
Thai PIT allowances (personal and family, insurance, retirement savings,
Thai ESG/ESGX, social security, home loan interest, donations, income
exemptions, stimulus measures) plus the Sec. 42 bis expense deduction.

Category caps follow HRMS validation: a sub-category max must not exceed
its category max and the declaration caps the category total, so groups
with a real combined limit carry it, groups without one use the sum of
their sub caps, and uncapped per-person/percentage items live in 0-cap
categories. Social Security uses the 2026 ceiling (10,500/yr); SSF is
kept inactive. sync_fixtures skips these files on sites without hrms.

default_thai_company/hooks.py

@@ -105,6 +105,9 @@ fixtures = [
 		],
 	},
 	{"doctype": "Tax Withholding Category", "filters": [["name", "like", "WHT %"]]},
+	# HRMS doctypes; skipped by sync_fixtures on sites without hrms
+	{"doctype": "Employee Tax Exemption Category"},
+	{"doctype": "Employee Tax Exemption Sub Category"},
 ]
 
 # Installation