feat(beheer): stamdata deletion protection — CI referential gate + editor expire/warn

CI gate (authoritative): generalize the dangling-reference test in StamdataValidationTests
into a declared, extensible reference list ("every declared reference into a stamdata key
resolves against the currently-valid stamdata"), starting with Diploma.Opleiding →
professions.program. Removing/renaming a referenced program, or expiring it while current
data still references it, fails the PR build (ADR-0004). Editor (fast feedback): confirm
before delete (warns a referenced row fails CI) and, for temporal tables, a "Sluiten per
vandaag" action that closes validity (geldigTot) — steering to expire over hard delete.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/locale/messages.en.xlf

@@ -3016,6 +3016,14 @@
           <context context-type="linenumber">226</context>
         </context-group>
       </trans-unit>
+      <trans-unit id="beheer.expire" datatype="html">
+        <source>Sluiten per vandaag</source>
+        <target datatype="html">Close as of today</target>
+      </trans-unit>
+      <trans-unit id="beheer.removeConfirm" datatype="html">
+        <source>Rij verwijderen? Als andere gegevens ernaar verwijzen, faalt de build-controle (CI). Bij een tabel met een geldigheidsperiode kunt u de rij beter sluiten (geldig tot) in plaats van verwijderen.</source>
+        <target datatype="html">Delete this row? If other data references it, the build check (CI) will fail. For a table with a validity period, prefer closing the row (valid until) over deleting it.</target>
+      </trans-unit>
 <trans-unit id="beheer.addRow" datatype="html">
         <source>Rij toevoegen</source>
         <target datatype="html">Add row</target>