fix(qml): 主窗口默认高 940 + 参考图回调 230，三段比例舒展

- Main.qml 登录态 height 880 → 940, minimumHeight 760 → 820
- 参考图 Card preferredHeight 170 → 230, minimum 160 → 200
- 视觉：参考图 / 提示词+设置 / 预览 ≈ 230 / 290 / 240，比例协调

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

@@ -13,8 +13,8 @@ Item {
         // ===== 参考图片卡片 =====
         Card {
             Layout.fillWidth: true
-            Layout.preferredHeight: 170
-            Layout.minimumHeight: 160
+            Layout.preferredHeight: 230
+            Layout.minimumHeight: 200
 
             ColumnLayout {
                 anchors.fill: parent

@@ -29,9 +29,9 @@ ApplicationWindow {
     function updateGeometry() {
         if (appState.loggedIn) {
             window.minimumWidth = 1100
-            window.minimumHeight = 760
+            window.minimumHeight = 820
             window.width = 1280
-            window.height = 880
+            window.height = 940
         } else {
             window.minimumWidth = 360
             window.minimumHeight = 420