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/invoice.py

@@ -44,8 +44,8 @@ class InvoiceFilter(BaseModel):
     """Filtru pentru căutarea facturilor"""
     company: str = Field(description="Codul firmei (schema Oracle)")
     partner_type: Literal["CLIENTI", "FURNIZORI"] = Field(description="Tipul partenerului")
-    date_from: Optional[date] = Field(description="Data de început")
-    date_to: Optional[date] = Field(description="Data de sfârșit")
+    luna: Optional[int] = Field(default=None, ge=1, le=12, description="Luna contabilă (1-12)")
+    an: Optional[int] = Field(default=None, ge=2000, le=2100, description="Anul contabil")
     partner_name: Optional[str] = Field(description="Filtru după nume")
     cont: Optional[str] = Field(description="Filtru după cont contabil")
     only_unpaid: bool = Field(default=True, description="Doar neachitate")