Fix Log Material dropdown invisible in dark mode

Replace hardcoded #fff / #f8f9fa / #dee2e6 / #e8eeff colors with Bootstrap
CSS variables so the dropdown respects the active theme.

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

src/PowderCoating.Web/Views/Jobs/Details.cshtml

@@ -1128,7 +1128,7 @@
                                             </button>
                                         </div>
                                         <div id="lmItemDropdown"
-                                             style="display:none;max-height:220px;overflow-y:auto;z-index:1070;background:#fff;border:1px solid rgba(0,0,0,.15);border-radius:.375rem;box-shadow:0 4px 12px rgba(0,0,0,.12);">
+                                             style="display:none;max-height:220px;overflow-y:auto;z-index:1070;background:var(--bs-body-bg);color:var(--bs-body-color);border:1px solid var(--bs-border-color);border-radius:.375rem;box-shadow:0 4px 12px rgba(0,0,0,.12);">
                                         </div>
                                     </div>
                                     <div id="lmItemBalance" class="form-text text-muted d-none"></div>