fix(api): [AB#266] mobile bug fixes — Stripe null guard, audit log, QuickBooks config

[bllr777]

Changes

• Guard null \InvoiceId\ in Stripe payment intent metadata to prevent crash when no invoice is linked
• Enrich audit log with user display name and org name (falls back to email when no display name)
• Add \QuickBooksSettings\ section to \�ppsettings.Development.json\ as configuration skeleton (AB#151)

Testing

• Build passes (0 warnings, 0 errors)
• Manual: verified Stripe payment intent created without \InvoiceId\ no longer throws