[IMP] l10n_at_hr_payroll_private: add statutory old-system severance (AP15-A)

Pay the pre-2003 AngG severance from the end-of-employment run as its own neutral benefit line: free of SV (§ 49 Abs 3 Z 7 ASVG) and payroll levies, outside the annual sixth, and collected into the § 291d EO termination pot net of its own wage tax. Taxation follows the binding better-of rule of § 67 Abs 3 EStG: multiple-of-method (tariff wage tax on the running monthly wage × the statutory multiple of the payout) versus the flat 6 % rate, applied mandatorily in favour of the employee. The tariff wage tax is captured as a separately confirmed value instead of deriving it from gross pay through the § 62 engine. The wizard enforces § 23a Abs 3 AngG (parental exit needs five uninterrupted years), blocks BMSVG-new contracts except frozen claims and validates AGRD 02/06 against the claim type. The LNK basis subtracts § 67 Abs 3/6 rules only when they actually run in the tax base, the L16 generator reports LST_ABF in key 260 outside 210/220, and result_rules access in the garnishment paths avoids DefaultDictPayroll materialisation. Verified against the original statute texts in .ris/ (AngG §§ 23/23a, EStG § 67 Abs 3).

Version 19.0.13.0.0 (private), 19.0.9.0.0 (core)

addons/l10n_at_hr_payroll/__manifest__.py

@@ -1,7 +1,7 @@
 # Part of the odoo-at-payroll project. License: LGPL-3.
 {
     'name': 'Österreich - Personalverrechnung Kern (AT Payroll Core)',
-    'version': '19.0.8.0.0',
+    'version': '19.0.9.0.0',
     'author': 'Florian Egger',
     'website': 'https://gem360.at',
     'category': 'Human Resources/Payroll',