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/Controllers/FormulaLibraryController.cs

@@ -0,0 +1,109 @@
+using AutoMapper;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using PowderCoating.Application.Interfaces;
+using PowderCoating.Core.Interfaces;
+using PowderCoating.Shared.Constants;
+
+namespace PowderCoating.Web.Controllers;
+
+/// <summary>
+/// Community formula library — browse published formulas from all companies and import
+/// them into the current company's local template list.
+/// </summary>
+[Authorize(Policy = AppConstants.Policies.CanViewData)]
+public class FormulaLibraryController : Controller
+{
+    private readonly IFormulaLibraryService _libraryService;
+    private readonly ITenantContext _tenantContext;
+    private readonly IMapper _mapper;
+    private readonly IAzureBlobStorageService _blobStorage;
+
+    public FormulaLibraryController(
+        IFormulaLibraryService libraryService,
+        ITenantContext tenantContext,
+        IMapper mapper,
+        IAzureBlobStorageService blobStorage)
+    {
+        _libraryService = libraryService;
+        _tenantContext = tenantContext;
+        _mapper = mapper;
+        _blobStorage = blobStorage;
+    }
+
+    /// <summary>Browse the community library with optional search and filter params.</summary>
+    // GET: /FormulaLibrary
+    public async Task<IActionResult> Index(
+        string? search = null,
+        string? outputMode = null,
+        string? industryHint = null)
+    {
+        var companyId = _tenantContext.GetCurrentCompanyId();
+        if (companyId == null) return RedirectToAction("Index", "Home");
+
+        var items = await _libraryService.BrowseAsync(companyId.Value, search, outputMode, industryHint);
+
+        ViewBag.Search = search;
+        ViewBag.OutputMode = outputMode;
+        ViewBag.IndustryHint = industryHint;
+        ViewBag.TotalCount = items.Count();
+
+        return View(items);
+    }
+
+    /// <summary>Returns full detail JSON for the import preview modal.</summary>
+    // GET: /FormulaLibrary/Detail/5
+    [HttpGet]
+    public async Task<IActionResult> Detail(int id)
+    {
+        var companyId = _tenantContext.GetCurrentCompanyId();
+        if (companyId == null) return Json(new { error = "No company context." });
+
+        var detail = await _libraryService.GetDetailAsync(id, companyId.Value);
+        if (detail == null) return NotFound();
+
+        return Json(detail);
+    }
+
+    /// <summary>
+    /// Serves a formula diagram image by blob storage path. Used for library cards where the
+    /// diagram belongs to another company's template blob container.
+    /// </summary>
+    // GET: /FormulaLibrary/Diagram?path=...
+    [HttpGet]
+    public async Task<IActionResult> Diagram(string path)
+    {
+        if (string.IsNullOrWhiteSpace(path)) return NotFound();
+
+        // Sanitize: path must not escape the blob container
+        if (path.Contains("..") || path.StartsWith("/") || path.StartsWith("\\"))
+            return BadRequest();
+
+        var (ok, bytes, contentType, _) = await _blobStorage.DownloadAsync("formulatemplate-diagrams", path);
+        if (!ok || bytes == null || bytes.Length == 0) return NotFound();
+        return File(bytes, contentType ?? "image/jpeg");
+    }
+
+    /// <summary>Imports a library entry as a new local template for the current company.</summary>
+    // POST: /FormulaLibrary/Import
+    [HttpPost]
+    [ValidateAntiForgeryToken]
+    [Authorize(Policy = AppConstants.Policies.CompanyAdminOnly)]
+    public async Task<IActionResult> Import(int libraryItemId)
+    {
+        var companyId = _tenantContext.GetCurrentCompanyId();
+        if (companyId == null)
+            return Json(new { success = false, message = "No company context." });
+
+        try
+        {
+            var userId = User.FindFirst(System.Security.Claims.ClaimTypes.NameIdentifier)?.Value ?? "";
+            var templateId = await _libraryService.ImportAsync(libraryItemId, companyId.Value, userId);
+            return Json(new { success = true, templateId });
+        }
+        catch (Exception ex)
+        {
+            return Json(new { success = false, message = ex.Message });
+        }
+    }
+}