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/Helpers/HelpKnowledgeBase.cs

@@ -1436,6 +1436,15 @@ public static class HelpKnowledgeBase
         Walkthrough: first time opening Custom Formulas tab with no templates triggers a 7-step guided tour automatically; also accessible via "How it works" button
         Help article: Help → Custom Formula Item Templates
 
+        **Community Formula Library (Company Settings → Custom Formulas → Community Library button):**
+        Platform-wide library where companies share their custom formula templates with all Powder Coating Logix users.
+        - Sharing: in the Library column on the Custom Formulas tab, click Share → add optional Tags and Industry Hint → Publish to Library. Eligible templates: ones created from scratch, or imported templates the company has since modified. Unmodified copies of another company's formula cannot be re-shared.
+        - Browsing: open via Community Library button on Custom Formulas tab → search by name/description/tags, filter by Output Mode or Industry → click Preview & Import to see full fields, formula expression, and diagram.
+        - Importing: click Import to My Formulas in the preview modal → a fully independent copy is added to your local library; edits to the copy do not affect the original. If the original creator deletes their diagram image, the image is automatically cleared from all imported copies.
+        - Attribution: every card shows the source company name. If a company imports a formula, modifies it, and re-shares it, the card displays "Inspired by [original name] from [original company]".
+        - Your own shared formulas: appear in the library with a gold "Your Formula" badge; Manage button links back to Company Settings. To remove from the library, click Unshare in the Library column — existing imports are unaffected.
+        - Import counts are shown on each card and the library is sorted by popularity (most imported first).
+
         ---
 
         **Employee Timeclock (/Timeclock):**