feat(11-02): wire Region/PLZ/Bundesland filter into query builder + FilterPanel

TenderQueryDto gains validated plz (@MaxLength(5)), region, and
bundesland fields. buildTenderWhere adds three conditional AND-branches:
plz startsWith, bundesland exact-match against the now-backfilled indexed
column (Pitfall 1), and region startsWith (usable independent of the
bundesland column). FilterPanel gets a PLZ input and a 16-Land Bundesland
dropdown (mirrors NUTS1_BUNDESLAND — web/api are separate packages) that
write plz/bundesland into the URL searchParams; ResultsList already
forwards the full URLSearchParams to listTenders(), so no additional
fetch wiring was needed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/web/src/app/(portal)/modules/tender-radar/components/FilterPanel.tsx

@@ -9,7 +9,8 @@ import { useRouter, useSearchParams } from 'next/navigation';
  * The `deadlineFrom`/`deadlineTo` param names deliberately match the
  * TenderQueryDto field names exactly — the Saved-Search serialization
  * contract in Plan 11-06 depends on the URL param names and the DTO field
- * names being identical strings (11-01-PLAN.md action note).
+ * names being identical strings (11-01-PLAN.md action note). `plz` and
+ * `bundesland` (Plan 11-02) follow the same convention.
  *
  * Hardcoded German strings — i18n rollout is Phase 14 (Research Open
  * Question 3, RESOLVED).
@@ -21,6 +22,32 @@ const SORT_OPTIONS: Array<{ value: string; label: string }> = [
   { value: 'value', label: 'Auftragswert' },
 ];
 
+/**
+ * Mirrors apps/api/src/tenders/geo/nuts-bundesland.ts's NUTS1_BUNDESLAND
+ * values (web and api are separate packages — no shared module for this
+ * small, stable 16-entry list; RESEARCH's "kleine Konstante spiegeln"
+ * option, FILTER-02 Plan 11-02 Task 3). Keep in sync if the Bundesland set
+ * ever changes (it will not — this is the fixed EU NUTS-1/DE schema).
+ */
+const BUNDESLAND_OPTIONS: string[] = [
+  'Baden-Württemberg',
+  'Bayern',
+  'Berlin',
+  'Brandenburg',
+  'Bremen',
+  'Hamburg',
+  'Hessen',
+  'Mecklenburg-Vorpommern',
+  'Niedersachsen',
+  'Nordrhein-Westfalen',
+  'Rheinland-Pfalz',
+  'Saarland',
+  'Sachsen',
+  'Sachsen-Anhalt',
+  'Schleswig-Holstein',
+  'Thüringen',
+];
+
 export function FilterPanel() {
   const router = useRouter();
   const searchParams = useSearchParams();
@@ -31,6 +58,8 @@ export function FilterPanel() {
   const openOnly = searchParams.get('openOnly') !== 'false';
   const deadlineFrom = searchParams.get('deadlineFrom') ?? '';
   const deadlineTo = searchParams.get('deadlineTo') ?? '';
+  const plz = searchParams.get('plz') ?? '';
+  const bundesland = searchParams.get('bundesland') ?? '';
 
   const setParam = (key: string, value: string | null) => {
     const next = new URLSearchParams(searchParams.toString());
@@ -124,6 +153,43 @@ export function FilterPanel() {
           />
         </div>
       </div>
+
+      <div className="flex flex-wrap items-end gap-4">
+        <div>
+          <label htmlFor="tr-filter-plz" className={labelCls}>
+            PLZ
+          </label>
+          <input
+            id="tr-filter-plz"
+            type="text"
+            inputMode="numeric"
+            maxLength={5}
+            placeholder="z. B. 10"
+            value={plz}
+            onChange={(e) => setParam('plz', e.target.value)}
+            className="h-9 w-28 rounded border border-border bg-background px-3 text-sm text-foreground"
+          />
+        </div>
+
+        <div className="min-w-[220px]">
+          <label htmlFor="tr-filter-bundesland" className={labelCls}>
+            Bundesland
+          </label>
+          <select
+            id="tr-filter-bundesland"
+            value={bundesland}
+            onChange={(e) => setParam('bundesland', e.target.value || null)}
+            className="h-9 w-full rounded border border-border bg-background px-3 text-sm text-foreground"
+          >
+            <option value="">Alle Bundesländer</option>
+            {BUNDESLAND_OPTIONS.map((name) => (
+              <option key={name} value={name}>
+                {name}
+              </option>
+            ))}
+          </select>
+        </div>
+      </div>
     </div>
   );
 }