feat: Add Trial Balance (Balanță de Verificare) feature

Comprehensive implementation of Trial Balance page with filtering,
pagination, and sorting capabilities.

Backend Changes:
- Added Pydantic models for Trial Balance (trial_balance.py)
  - TrialBalanceItem: Individual balance record
  - TrialBalanceFilters: Filter parameters
  - TrialBalancePagination: Pagination metadata
  - TrialBalanceResponse: Complete API response
- Created FastAPI router (/api/trial-balance) with:
  - Filtering by account number (cont) and description (denumire)
  - Pagination support (configurable page size)
  - Sorting on all columns (ascendent/descendent)
  - Company-based access control via JWT
  - Query against Oracle VBAL table
- Registered router in main.py

Frontend Changes:
- Created Pinia store (trialBalanceStore.js) with:
  - State management for trial balance data
  - Filters (luna, an, cont, denumire)
  - Pagination controls
  - Sorting functionality
  - Error handling and loading states
- Built TrialBalanceView.vue component featuring:
  - PrimeVue DataTable with responsive design
  - Period display (month/year)
  - Dual input filters (account number + description)
  - Debounced search (500ms)
  - Clear filters functionality
  - Formatted currency display (Romanian locale)
  - Balance columns (Debit/Credit) for:
    - Sold Precedent (Previous Balance)
    - Rulaj Lunar (Monthly Movement)
    - Sold Final (Final Balance)
  - Loading spinner and empty state
  - Mobile-friendly responsive layout
- Added route: /trial-balance with auth guard
- Added menu item in HamburgerMenu (Navigation section)
  - Icon: pi-calculator
  - Label: "Balanță de Verificare"

Technical Details:
- Follows established CSS architecture (no :deep(), uses design tokens)
- Consistent with InvoicesView patterns
- Implements proper error handling
- Uses Oracle NVL for null value handling
- ROW_NUMBER pagination for Oracle compatibility

Testing: Manual testing required (Phase 5)

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

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

reports-app/frontend/src/components/layout/HamburgerMenu.vue

@@ -46,6 +46,17 @@
               <span>Bank & Cash</span>
             </router-link>
           </li>
+          <li class="menu-item">
+            <router-link
+              to="/trial-balance"
+              class="menu-link"
+              :class="{ active: $route.name === 'TrialBalance' }"
+              @click="closeMenu"
+            >
+              <i class="menu-icon pi pi-calculator"></i>
+              <span>Balanță de Verificare</span>
+            </router-link>
+          </li>
         </ul>
       </div>