docs: add UI/UX component guidelines and improve breadcrumb/tab-panel styling

Add "Komponenten in Formularen" section to boundaries-ui.md with rules
for core button classes, margin resets, checkbox sizing, sticky positioning,
icon-only buttons, responsive grids, and CSS variables. Add matching
quick-reference bullets to CLAUDE.md UI Patterns section.

Fix breadcrumb wrapping: nowrap + overflow hidden + flex-shrink for
single-line behavior. Add data-tab-panel-wide opt-out for full-width
tab panels (default 70ch).

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

web/css/components/app-details.css

@@ -8,6 +8,10 @@
     max-width: 70ch;
   }
 
+  .app-details-container > section > form [data-tab-panel-wide] {
+    max-width: none;
+  }
+
   .app-details-aside-actions {
     display: grid;
     gap: calc(var(--app-spacing) * 0.5);