vitec_card: flipcard layout + card-back fields; shared-column repair

- layout_variant gains the value "flipcard" (onChange: reload)
- "Card Back" palette in the Layout tab directly below layout_variant:
  back_headline (Text, max 100) and back_text (Textarea, richtext),
  displayCond-gated on the flipcard layout; serialised unconditionally -
  the frontend keys the back face on layout_variant, not on field
  presence (spec 7.7)
- backend preview: flipcard badge + back-headline line
- repair "[ Missing label ]" in the card selects: layout_variant /
  background_variant are columns SHARED with vitec_ctabanner, and the
  index-wise Content Blocks merge dropped four card-only values from
  the base item list. Overrides/tt_content.php now pins the base column
  to the cta-banner lists and hands vitec_card its full lists via
  columnsOverrides (respected by FormEngine and DataHandler; an items
  override can only extend, never shorten - array_replace_recursive)
- spec v1.19 incl. head-matter fix (version table was stuck at 1.17)

Server follow-up: database:updateschema "*.add,*.change" + cache:flush

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/vitec/ContentBlocks/ContentElements/card/language/labels.xlf

@@ -54,6 +54,19 @@
         <source>If set, the whole card becomes clickable. Overrides individual CTAs visually in the frontend.</source>
       </trans-unit>
 
+      <trans-unit id="back_headline.label">
+        <source>Back Headline</source>
+      </trans-unit>
+      <trans-unit id="back_headline.description">
+        <source>Headline on the reverse side of the card. Only used by the Flip Card layout.</source>
+      </trans-unit>
+      <trans-unit id="back_text.label">
+        <source>Back Text</source>
+      </trans-unit>
+      <trans-unit id="back_text.description">
+        <source>Text on the reverse side of the card. Only used by the Flip Card layout.</source>
+      </trans-unit>
+
       <!-- ============================================================== -->
       <!-- layout_variant                                                  -->
       <!-- ============================================================== -->
@@ -84,6 +97,9 @@
       <trans-unit id="layout_variant.items.compact.label">
         <source>Compact (small card, tight spacing)</source>
       </trans-unit>
+      <trans-unit id="layout_variant.items.flipcard.label">
+        <source>Flip Card (front / back)</source>
+      </trans-unit>
 
       <!-- ============================================================== -->
       <!-- background_variant                                              -->