Condense Operations sidebar: remove 5 items, tighten padding

Layer 1 — relocate off nav:
  Shop Display + Shop Mobile → Jobs page header (split dropdown on Blank Work Order)
  Powder Insights → Inventory page header button

Layer 2 — remove orphan section headers:
  "Main Menu" (only had Dashboard under it)
  "Reports" (only had Reports link under it)

Layer 3 — CSS density:
  nav-link padding 0.75rem → 0.55rem vertical
  nav-section-title padding 1rem/0.5rem → 0.65rem/0.3rem

Operations mode: 27 elements → 22. Scrollbar eliminated on standard screens.

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

src/PowderCoating.Web/Views/Inventory/Index.cshtml

@@ -15,6 +15,9 @@
         <a asp-action="Ledger" class="btn btn-outline-secondary">
             <i class="bi bi-journal-text me-2"></i>Inventory Activity
         </a>
+        <a asp-controller="PowderInsights" asp-action="Index" class="btn btn-outline-secondary" title="Powder usage analytics">
+            <i class="bi bi-graph-up me-2"></i>Powder Insights
+        </a>
         <a asp-action="SamplePanels" class="btn btn-outline-primary">
             <i class="bi bi-palette me-2"></i>Manage Sample Panels
         </a>