[devmount]

Description of the Change

Expense categories now have a description, taken from the wording of the Elster form "Anlage EÜR, 4 – 2. Betriebsausgaben", so it's easier to choose the category that is correct for the tax return.

• ExpenseCategory implements Filament's HasDescription contract with a translated getDescription() method (en/de). The minor-assets limit in its text is read from config('business.minor_assets.max_net').
• Expense form: the category select shows the description of the selected category as help text and updates it live when the category changes.
• Expense table: hovering a category badge shows its description as a tooltip.

While mapping the categories to the EÜR lines, it turned out that the Vat category was missing from the tax return widget:

• TaxReturnFormInput has two new rows:
  • EÜR line 58 (VAT paid to the tax office): the sum of positive Vat expenses.
  • EÜR line 18 (VAT refunded by the tax office): the sum of negative Vat expenses, shown as a positive amount. Negative entries are already created by Expense::saveLastAdvanceVat() in refund months.
• The final profit line (rsc97) now includes both lines, matching Elster's calculation.
• The taxable toggle is disabled and saved as false when a tax category (Vat, Tax) is selected. A tax payment or refund contains no VAT itself, and a taxable entry would only report its net amount on line 58/18.

Also fixes the three remaining Pint formatting issues (method ordering and line wrapping only, no behaviour change).

Benefits

• No more guessing which category an expense belongs to for the tax return.
• The tax return widget covers VAT payments and refunds, and its profit line matches what Elster calculates.
• The codebase passes Pint again.

Applicable Issues

Closes #203