feat: BackupService real pg_dump, OrganisationService region stats, SystemConfigService overrides

- BackupService: DB-persisted metadata (BackupRecord/BackupConfig entities + V16 Flyway migration),
  real pg_dump execution via ProcessBuilder, soft-delete on deleteBackup, pg_restore manual guidance
- OrganisationService: repartitionRegion now queries Adresse entities (was Map.of() stub)
- SystemConfigService: in-memory config overrides via AtomicReference (no DB dependency)
- SystemMetricsService: null-guard on MemoryMXBean in getSystemStatus() (fixes test NPE)
- Souscription workflow: SouscriptionService, SouscriptionResource, FormuleAbonnementRepository,
  V11 Flyway migration, admin REST clients
- Flyway V8-V15: notes membres, types référence, type orga constraint, seed roles,
  première connexion, Wave checkout URL, Wave telephone column length fix
- .gitignore: added uploads/ and .claude/

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main/java/dev/lions/unionflow/server/service/BudgetService.java

@@ -322,7 +322,9 @@ public class BudgetService {
             // Champs calculés
             .realizationRate(budget.getRealizationRate())
             .variance(budget.getVariance())
-            .varianceRate(budget.getVariance().doubleValue() / budget.getTotalPlanned().doubleValue() * 100)
+            .varianceRate(budget.getTotalPlanned() != null && budget.getTotalPlanned().doubleValue() > 0
+                    ? budget.getVariance().doubleValue() / budget.getTotalPlanned().doubleValue() * 100
+                    : 0.0)
             .isOverBudget(budget.isOverBudget())
             .isActive(budget.isActive())
             .isCurrentPeriod(budget.isCurrentPeriod())