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.Infrastructure/Repositories/UnitOfWork.cs

@@ -130,6 +130,10 @@ public class UnitOfWork : IUnitOfWork
     // Custom Formula Templates
     private IRepository<CustomItemTemplate>? _customItemTemplates;
 
+    // Formula Community Library
+    private IPlainRepository<FormulaLibraryItem>? _formulaLibrary;
+    private IRepository<FormulaLibraryImport>? _formulaLibraryImports;
+
     // Purchase Orders
     private IPurchaseOrderRepository? _purchaseOrders;
     private IRepository<PurchaseOrderItem>? _purchaseOrderItems;
@@ -476,6 +480,14 @@ public class UnitOfWork : IUnitOfWork
     public IRepository<CustomItemTemplate> CustomItemTemplates =>
         _customItemTemplates ??= new Repository<CustomItemTemplate>(_context);
 
+    /// <summary>Repository for <see cref="FormulaLibraryItem"/> community library entries; platform-level, no tenant filter.</summary>
+    public IPlainRepository<FormulaLibraryItem> FormulaLibrary =>
+        _formulaLibrary ??= new PlainRepository<FormulaLibraryItem>(_context);
+
+    /// <summary>Repository for <see cref="FormulaLibraryImport"/> per-company import records; tenant-filtered with soft delete.</summary>
+    public IRepository<FormulaLibraryImport> FormulaLibraryImports =>
+        _formulaLibraryImports ??= new Repository<FormulaLibraryImport>(_context);
+
     // Job Templates
     /// <summary>Repository for <see cref="JobTemplate"/> reusable job blueprints; tenant-filtered with soft delete.</summary>
     public IJobTemplateRepository JobTemplates =>