fix: align send button vertically centered with pill input

- .input-row: align-items center, gap 8px
- .pill-send-btn: align-self center on wrapper (not button)
- remove flex-end and margin-bottom that caused top misalignment

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

app.py

@@ -552,6 +552,7 @@ footer { display: none !important; }
     outline: none !important;
     box-shadow: 0 0 0 3px rgba(59,130,246,.12) !important;
 }
+.pill-send-btn { align-self: center !important; }
 .pill-send-btn button {
     border-radius: 50% !important;
     width: 48px !important;
@@ -559,10 +560,11 @@ footer { display: none !important; }
     min-width: 48px !important;
     padding: 0 !important;
     font-size: 1.3rem !important;
-    align-self: flex-end !important;
-    margin-bottom: 2px !important;
 }
 
+/* ── 입력 Row 세로 중앙 정렬 ── */
+.input-row { align-items: center !important; gap: 8px !important; }
+
 /* ── 예시 질문 Chip (D4-4) ── */
 .example-chips-row { padding: 6px 0 4px !important; flex-wrap: wrap !important; gap: 8px !important; }
 .example-chip-btn button {