feat: Add actionable hints to all 138 compliance checks

Each check now has a "hint" field explaining what is missing and
what the customer should do to fix it. Hints are shown in the
frontend below failed checks in red text.

Examples:
- "Bei Verarbeitung auf Basis von Art. 6(1)(f) muss dokumentiert
  werden, warum Ihr berechtigtes Interesse die Rechte der
  Betroffenen ueberwiegt."
- "Die ladungsfaehige Anschrift fehlt. Erforderlich: Strasse,
  Hausnummer, PLZ und Ort."

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

admin-compliance/app/sdk/agent/_components/ChecklistView.tsx

@@ -11,6 +11,7 @@ interface CheckItem {
   level?: number
   parent?: string | null
   skipped?: boolean
+  hint?: string
 }
 
 interface DocResult {
@@ -177,6 +178,11 @@ export function ChecklistView({ results }: { results: DocResult[] }) {
                                   "...{g.check.matched_text}..."
                                 </div>
                               )}
+                              {!g.check.passed && g.check.hint && (
+                                <div className="text-xs text-red-600/80 mt-0.5">
+                                  {g.check.hint}
+                                </div>
+                              )}
                             </div>
                           </div>
 
@@ -199,6 +205,11 @@ export function ChecklistView({ results }: { results: DocResult[] }) {
                                         &quot;...{ch.matched_text}...&quot;
                                       </div>
                                     )}
+                                    {!ch.passed && !ch.skipped && ch.hint && (
+                                      <div className="text-xs text-red-500/80 mt-0.5">
+                                        {ch.hint}
+                                      </div>
+                                    )}
                                   </div>
                                 </div>
                               ))}