feat: Add accounting period selector for all views

- Add PeriodSelectorMini component for global period selection
- Add accountingPeriod store for shared period state
- Add calendar service/router/model for available periods API
- Update Dashboard, Invoices, Trial Balance, Bank/Cash Register views
  to respect selected period
- Fix Trial Balance navigation sync bug (period now syncs on mount)
- Update backend services to accept luna/an parameters

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

reports-app/backend/app/models/treasury.py

@@ -25,6 +25,8 @@ class RegisterFilter(BaseModel):
     """Filtre pentru registrul de casă și bancă"""
     company: str
     register_type: Optional[str] = None  # BANCA_LEI, BANCA_VALUTA, CASA_LEI, CASA_VALUTA sau None pentru toate
+    luna: Optional[int] = None  # Luna contabilă (1-12) pentru PACK_SESIUNE
+    an: Optional[int] = None  # Anul contabil pentru PACK_SESIUNE
     date_from: Optional[datetime] = None
     date_to: Optional[datetime] = None
     partner_name: Optional[str] = None