UX-MOBILE-1: FilterPanel — einklappbare Filter auf Mobil (390px)

Neues FilterPanel-Muster (src/components/FilterPanel.tsx + filterPanel.css):
- Mobil (<768px): Suchfeld immer sichtbar; alle weiteren Filter hinter einem
  'Filter (N)'-Button eingeklappt (Badge = Anzahl aktiver Nicht-Default-Filter).
  Tippen öffnet/schließt den Drawer. 'Filter zurücksetzen' im Drawer.
- Desktop (>=768px): Toggle versteckt, Drawer als display:contents → alle Controls
  inline in der bestehenden .filters-Flexzeile, wie bisher.
Auf GerbilsPage, WuerfeListPage und AnfragenPage ausgerollt.
BeckenPage/KontaktePage nur ein Suchfeld → kein Panel nötig.

e2e: filter-panel.spec.ts (8 Tests, phone+desktop); bestand/tiere/anfragen-Specs
erhalten openFilterPanel-Aufruf vor Drawer-Controls; fixtures.ts +openFilterPanel().
Vitest 78 / e2e 102 grün.

Mobil-Pass (390px, Durchsicht): Hauptproblem behoben. Beobachtete Restpunkte
für god (nicht selbst gefixed):
- .genotype-table in Genetik/Probeverpaarung: Genotyp-Strings können eng werden
- Stammbaum (react-d3-tree SVG): kein explizites mobile Viewport-Handling
- BreedingResultView Genotyp-Detail-Tabelle: ggf. horizontal scrollbar-los

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

gerbil-manager-web/src/components/FilterPanel.tsx

@@ -0,0 +1,52 @@
+import { useState, type ReactNode } from 'react'
+import { de } from '../strings/de'
+import './filterPanel.css'
+
+interface FilterPanelProps {
+  /** Always visible on mobile (typically the search text input). Optional. */
+  searchField?: ReactNode
+  /** Collapsible filters (hidden behind toggle on mobile; inline on desktop). */
+  children: ReactNode
+  /** Number of currently active (non-default) filter values. Shown as badge. */
+  activeCount: number
+  /** Called when the reset button is clicked. */
+  onReset: () => void
+}
+
+/**
+ * UX-MOBILE-1: wraps a set of filter controls so they collapse on mobile.
+ * Render inside the existing `.filters` div (or replace it entirely).
+ *
+ * Desktop (>=768px): renders all children inline, identical to today.
+ * Mobile (<768px): shows searchField + a "Filter (N)" toggle; tapping reveals
+ *   the rest of the controls in a column drawer + a reset button.
+ */
+export function FilterPanel({ searchField, children, activeCount, onReset }: FilterPanelProps) {
+  const [open, setOpen] = useState(false)
+  const t = de.filterPanel
+
+  const label = activeCount > 0 ? `${t.toggleButton} (${activeCount})` : t.toggleButton
+
+  return (
+    <div className={`filters filter-panel${open ? ' filter-panel--open' : ''}`}>
+      {searchField}
+      <button
+        type="button"
+        className="btn btn--ghost filter-panel__toggle"
+        onClick={() => setOpen((v) => !v)}
+        aria-expanded={open}
+        aria-label={label}
+      >
+        {label}
+      </button>
+      <div className="filter-panel__drawer">
+        {children}
+        {activeCount > 0 && (
+          <button type="button" className="btn btn--ghost filter-panel__reset-btn" onClick={onReset}>
+            {t.resetButton}
+          </button>
+        )}
+      </div>
+    </div>
+  )
+}

gerbil-manager-web/src/components/filterPanel.css

@@ -0,0 +1,53 @@
+/*
+ * UX-MOBILE-1: FilterPanel — collapsible filter drawer on mobile.
+ *
+ * Desktop (>=768px): toggle hidden, drawer shows as display:contents so its
+ *   children participate directly in the parent .filters flex row.
+ * Mobile (<768px): searchField inline, then toggle button. Tap opens a full-
+ *   width drawer (flex column) with the remaining filters + reset button.
+ */
+
+/* ── Mobile default ── */
+.filter-panel__toggle {
+  display: inline-flex;
+  align-items: center;
+  gap: 0.25rem;
+  white-space: nowrap;
+}
+
+.filter-panel__drawer {
+  display: none;
+  flex-direction: column;
+  gap: 0.75rem;
+  width: 100%;
+  padding-top: 0.25rem;
+}
+
+.filter-panel--open .filter-panel__drawer {
+  display: flex;
+}
+
+/* ── Desktop ── */
+@media (min-width: 768px) {
+  .filter-panel__toggle {
+    display: none;
+  }
+
+  .filter-panel__drawer {
+    /* Let children participate directly in the parent flex row. */
+    display: contents;
+  }
+
+  /* Reset button sits in the flex row on desktop when active filters exist. */
+  .filter-panel__reset-btn {
+    align-self: flex-end;
+  }
+}
+
+/* ── Mobile reset button ── */
+@media (max-width: 767px) {
+  .filter-panel__reset-btn {
+    align-self: flex-start;
+    margin-top: 0.25rem;
+  }
+}