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.Application/DTOs/Company/FormulaLibraryDtos.cs

@@ -0,0 +1,69 @@
+namespace PowderCoating.Application.DTOs.Company;
+
+// ── Browse / card display ──────────────────────────────────────────────────
+
+/// <summary>Lean DTO for the community library browse grid card.</summary>
+public class FormulaLibraryCardDto
+{
+    public int Id { get; set; }
+    public string Name { get; set; } = string.Empty;
+    public string? Description { get; set; }
+    public string OutputMode { get; set; } = "FixedRate";
+    public string? Tags { get; set; }
+    public string? IndustryHint { get; set; }
+    public string SourceCompanyName { get; set; } = string.Empty;
+    public int ImportCount { get; set; }
+    public DateTime SharedAt { get; set; }
+    public string? DiagramImagePath { get; set; }
+
+    /// <summary>Non-null when this formula was derived from another library entry.</summary>
+    public int? InspiredByFormulaLibraryItemId { get; set; }
+    public string? InspiredByName { get; set; }
+    public string? InspiredByCompanyName { get; set; }
+
+    /// <summary>True when the current company has already imported this entry.</summary>
+    public bool AlreadyImported { get; set; }
+
+    /// <summary>True when this formula was shared by the current browsing company.</summary>
+    public bool IsOwnFormula { get; set; }
+}
+
+// ── Full detail (import preview modal) ────────────────────────────────────
+
+/// <summary>Full DTO used in the import preview modal — shows fields and formula.</summary>
+public class FormulaLibraryDetailDto : FormulaLibraryCardDto
+{
+    public string FieldsJson { get; set; } = "[]";
+    public string Formula { get; set; } = string.Empty;
+    public decimal? DefaultRate { get; set; }
+    public string? RateLabel { get; set; }
+    public string? Notes { get; set; }
+    public int FieldCount { get; set; }
+}
+
+// ── Share from Company Settings ───────────────────────────────────────────
+
+/// <summary>Submitted when a company admin shares one of their templates to the community library.</summary>
+public class ShareFormulaRequest
+{
+    public int CustomItemTemplateId { get; set; }
+    public string? Tags { get; set; }
+    public string? IndustryHint { get; set; }
+}
+
+// ── Company Settings list view ─────────────────────────────────────────────
+
+/// <summary>Status of a template relative to the community library, shown in Company Settings.</summary>
+public class FormulaLibraryStatusDto
+{
+    /// <summary>The FormulaLibraryItem Id, if this template has ever been shared.</summary>
+    public int? LibraryItemId { get; set; }
+    public bool IsPublished { get; set; }
+
+    /// <summary>Whether this template is eligible to be shared (original or modified import).</summary>
+    public bool CanShare { get; set; }
+
+    /// <summary>Set when this template was imported; the name of the original library entry.</summary>
+    public string? ImportedFromName { get; set; }
+    public string? ImportedFromCompany { get; set; }
+}

src/PowderCoating.Application/Interfaces/IFormulaLibraryService.cs

@@ -0,0 +1,51 @@
+using PowderCoating.Application.DTOs.Company;
+
+namespace PowderCoating.Application.Interfaces;
+
+/// <summary>
+/// Manages the community formula library: sharing, unsharing, importing, and browsing.
+/// </summary>
+public interface IFormulaLibraryService
+{
+    /// <summary>
+    /// Returns all published library entries, with AlreadyImported populated for the given company.
+    /// Optionally filters by search term, output mode, or industry hint.
+    /// </summary>
+    Task<IEnumerable<FormulaLibraryCardDto>> BrowseAsync(
+        int companyId,
+        string? search = null,
+        string? outputMode = null,
+        string? industryHint = null);
+
+    /// <summary>Full detail for the import preview modal, including field list and formula.</summary>
+    Task<FormulaLibraryDetailDto?> GetDetailAsync(int libraryItemId, int companyId);
+
+    /// <summary>
+    /// Publishes a company template to the community library.
+    /// If the template was previously shared and unpublished, re-publishes the existing row.
+    /// Updates the library entry fields from the current template state on re-share.
+    /// </summary>
+    Task<int> ShareAsync(int companyId, string userId, ShareFormulaRequest request);
+
+    /// <summary>Sets IsPublished = false. Existing imports are unaffected.</summary>
+    Task UnshareAsync(int libraryItemId, int companyId);
+
+    /// <summary>
+    /// Copies a library entry into the company's local CustomItemTemplate table.
+    /// If the company already has an import record for this entry, returns the existing template id.
+    /// </summary>
+    Task<int> ImportAsync(int libraryItemId, int companyId, string userId);
+
+    /// <summary>
+    /// Returns the library status for a given CustomItemTemplate — whether it is shared,
+    /// eligible to be shared, and where it was imported from if applicable.
+    /// </summary>
+    Task<FormulaLibraryStatusDto> GetTemplateLibraryStatusAsync(int templateId, int companyId);
+
+    /// <summary>
+    /// Nulls out DiagramImagePath on the FormulaLibraryItem and all imported copies
+    /// when a source template's diagram is removed. Call from CompanySettingsController
+    /// when a diagram is deleted or replaced.
+    /// </summary>
+    Task CascadeRemoveDiagramAsync(int sourceCustomItemTemplateId);
+}

src/PowderCoating.Application/Mappings/FormulaLibraryProfile.cs

@@ -0,0 +1,35 @@
+using AutoMapper;
+using PowderCoating.Core.Entities;
+using PowderCoating.Application.DTOs.Company;
+
+namespace PowderCoating.Application.Mappings;
+
+public class FormulaLibraryProfile : Profile
+{
+    public FormulaLibraryProfile()
+    {
+        CreateMap<FormulaLibraryItem, FormulaLibraryCardDto>()
+            .ForMember(dest => dest.InspiredByName,
+                opt => opt.MapFrom(src => src.InspiredBy != null ? src.InspiredBy.Name : null))
+            .ForMember(dest => dest.InspiredByCompanyName,
+                opt => opt.MapFrom(src => src.InspiredBy != null ? src.InspiredBy.SourceCompanyName : null))
+            .ForMember(dest => dest.AlreadyImported, opt => opt.Ignore()); // set by service
+
+        CreateMap<FormulaLibraryItem, FormulaLibraryDetailDto>()
+            .IncludeBase<FormulaLibraryItem, FormulaLibraryCardDto>()
+            .ForMember(dest => dest.FieldCount,
+                opt => opt.MapFrom(src => CountFields(src.FieldsJson)));
+    }
+
+    private static int CountFields(string fieldsJson)
+    {
+        try
+        {
+            var doc = System.Text.Json.JsonDocument.Parse(fieldsJson);
+            return doc.RootElement.ValueKind == System.Text.Json.JsonValueKind.Array
+                ? doc.RootElement.GetArrayLength()
+                : 0;
+        }
+        catch { return 0; }
+    }
+}