Allowance 1.0.6 — Next Payment column

Adds a sortable Next Payment column to the Allowance table. Dates and times use the browser's local timezone; missing or invalid values display a dash.

Validated with the dev Playwright create/edit/reload/delete flow and browser checks for valid, missing and invalid dates. All CI checks passed. Payment schedules and payment processing are unchanged.

The attached archive contains tested source revision dbb96ef, with its checksum recorded in extensions.json.