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/routers/treasury.py

@@ -16,6 +16,8 @@ router = APIRouter()
 async def get_bank_cash_register(
     company: str = Query(description="Codul firmei"),
     register_type: Optional[str] = Query(None, description="Tipul registrului: BANCA_LEI, BANCA_VALUTA, CASA_LEI, CASA_VALUTA sau None pentru toate"),
+    luna: Optional[int] = Query(None, ge=1, le=12, description="Luna contabilă (1-12)"),
+    an: Optional[int] = Query(None, ge=2000, le=2100, description="Anul contabil"),
     date_from: Optional[str] = Query(None, description="Data început (YYYY-MM-DD)"),
     date_to: Optional[str] = Query(None, description="Data sfârșit (YYYY-MM-DD)"),
     partner_name: Optional[str] = Query(None, description="Filtru nume partener"),
@@ -63,6 +65,8 @@ async def get_bank_cash_register(
         filter_params = RegisterFilter(
             company=company,
             register_type=register_type,
+            luna=luna,
+            an=an,
             date_from=date_from_obj,
             date_to=date_to_obj,
             partner_name=partner_name,