fix: restore Limite Quotidienne and complete admin i18n

feat: CSV export, monthly report, and quota alert plan filter

fix(audit): resolve remaining minor technical debt issues

feat(billing): refonte UX non-tech + enrichissement contexte IA

feat(billing): close 3 remaining wallet gaps from implementation plan

feat(billing): implement full wallet/ledger system with hard-stop enforcement

feat(billing): enforce AI credit limits across all surfaces

fix(admin): make all modals scrollable and responsive on mobile

feat(billing): complete billing system, push notifications, and tech debt fixes