Phase F: Add Invoice Write-Off, Fixed Assets, Period Locking, and 1099 Tracking

- Invoice Write-Off: WriteOff POST action in InvoicesController posts bad-debt JE
  (DR bad debt expense / CR AR), reduces customer balance, marks invoice WrittenOff;
  write-off modal added to Invoice Details view with expense account selector
- Fixed Assets: FixedAsset + FixedAssetDepreciationEntry entities with straight-line
  depreciation; FixedAssetsController (Index/Create/Edit/Details/PostDepreciation/Delete);
  PostDepreciation auto-generates one JE per asset per period, skips already-posted,
  fully-depreciated, and disposed assets; full CRUD views + nav link
- Period Locking: Company.BookLockedThrough field; AccountingPeriodValidator static helper;
  lock check added to JE Post and Bill Create (blocks backdating into closed periods);
  SetPeriodLock action + date picker UI in Company Settings Accounting section
- 1099 Tracking: Is1099Vendor flag on Vendor entity + DTOs; checkbox in Create/Edit views;
  TaxReporting1099 report action + view lists payments by year, flags vendors >= $600;
  report card added to Reports Landing
- Migration AddFixedAssetsLockAnd1099 applied

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

src/PowderCoating.Web/Views/Reports/Landing.cshtml

@@ -212,6 +212,14 @@
             <p>Track actual cash in/out across operating, investing, and financing activities with beginning and ending cash balance.</p>
             <div class="report-arrow">Open report <i class="bi bi-arrow-right"></i></div>
         </a>
+        <a asp-controller="Reports" asp-action="TaxReporting1099" class="report-card">
+            <div class="report-card-icon" style="background:#fdf2f8;color:#86198f;">
+                <i class="bi bi-file-earmark-text"></i>
+            </div>
+            <h5>1099-NEC Report</h5>
+            <p>Payments to 1099-eligible vendors by calendar year — flags those exceeding the $600 reporting threshold.</p>
+            <div class="report-arrow">Open report <i class="bi bi-arrow-right"></i></div>
+        </a>
     </div>
 </div>
 }