Add Community Formula Library feature

Companies can now share their custom formula templates to a platform-wide
community library. Other tenants can browse, preview, and import formulas
as independent local copies. Includes attribution (source company name),
"Inspired by" lineage for re-contributed formulas, import counts, own-formula
badge, cascade diagram nullification, and AI assistant + help docs updates.

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

src/PowderCoating.Web/Views/Shared/_Layout.cshtml

@@ -1504,7 +1504,7 @@ var hasReports = _isAdminOrManager || User.HasClaim("Permission", "ViewReports")
                                 {
                                     <li><a class="dropdown-item" asp-controller="CompanyUsers" asp-action="Index"><i class="bi bi-people-fill me-2"></i>Manage Users</a></li>
                                     <li><a class="dropdown-item" asp-controller="PricingTiers" asp-action="Index"><i class="bi bi-tags me-2"></i>Pricing Tiers</a></li>
-                                    <li><a class="dropdown-item" asp-controller="TaxRates" asp-action="Index"><i class="bi bi-percent me-2"></i>Tax Rates</a></li>
+<li><a class="dropdown-item" asp-controller="TaxRates" asp-action="Index"><i class="bi bi-percent me-2"></i>Tax Rates</a></li>
                                     <li><a class="dropdown-item" asp-controller="Kiosk" asp-action="Activate"><i class="bi bi-tablet me-2"></i>Kiosk Setup</a></li>
                                 }
                                 <li><hr class="dropdown-divider"></li>