feat: remove header row, add unlock gate + ring animation to Satz card

- Remove lang/points header from all 3 card types
- PairSentenceCard: Verstanden button locked until audio played OR
  translate button held for 2 seconds
- Hold button shows circular gold ring filling up over 2s while held
- TTS button highlights gold when unlocked
- .pair-btn-locked style for disabled state

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/PairCards.css

@@ -71,12 +71,31 @@
   cursor: pointer;
   padding: 0;
   flex-shrink: 0;
-  transition: background 0.15s;
+  transition: background 0.15s, color 0.15s;
+  color: #7A6E55;
   -webkit-user-select: none;
   user-select: none;
 }
 .pair-icon-btn:hover  { background: #E0DAC8; }
-.pair-icon-btn.active { background: #E0DAC8; }
+.pair-icon-btn.active { background: #C4A85A22; color: #B07840; }
+
+/* Hold-to-translate button */
+.pair-hold-wrap {
+  width: 38px;
+  height: 38px;
+  flex-shrink: 0;
+  cursor: pointer;
+  -webkit-user-select: none;
+  user-select: none;
+  border-radius: 10px;
+  overflow: visible;
+}
+
+/* Ring fill animation — 2 seconds */
+@keyframes holdRing {
+  from { stroke-dashoffset: 100.53; }
+  to   { stroke-dashoffset: 0; }
+}
 
 /* ── Image area ── */
 .pair-image-wrap {
@@ -278,6 +297,11 @@
   background: #5C3D22;
   color: #F5EDE0;
 }
+.pair-btn-locked {
+  background: #E0DDD5;
+  color: #B0A898;
+  cursor: not-allowed;
+}
 .pair-btn-yes {
   background: #3D7055;
   color: #fff;