feat: new-version hint text left of the gear (replaces red button)

Show a low-key blue, clickable "发现新版本 vX.Y.Z" label just left of the
⚙ 配置 button when an update is found (hidden otherwise), instead of recoloring
the button red. Matches docs/07 §4.3.

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

src/app/main_window.py

@@ -112,6 +112,14 @@ class MainWindow(QMainWindow):
         layout.addWidget(self._tab_bar)
         layout.addStretch()
 
+        # "New version" hint, just left of the gear; hidden until found (docs/07 §4.3)
+        self._update_hint = QPushButton("")
+        self._update_hint.setObjectName("updateHint")
+        self._update_hint.setCursor(Qt.PointingHandCursor)
+        self._update_hint.setVisible(False)
+        self._update_hint.clicked.connect(self._open_settings)
+        layout.addWidget(self._update_hint)
+
         # Right-aligned utility entry — not a numbered workflow step (docs/07 §4.3)
         self._settings_btn = QPushButton("⚙ 配置")
         self._settings_btn.setObjectName("settingsBtn")
@@ -175,12 +183,11 @@ class MainWindow(QMainWindow):
         self._set_update_indicator(True, info.version)
 
     def _set_update_indicator(self, available, version=""):
-        self._settings_btn.setText("⚙ 配置  ●" if available else "⚙ 配置")
-        self._settings_btn.setProperty("hasUpdate", bool(available))
-        self._settings_btn.setToolTip(
-            "发现新版本 v{}，点击进入设置更新".format(version) if available else "")
-        self._settings_btn.style().unpolish(self._settings_btn)
-        self._settings_btn.style().polish(self._settings_btn)
+        """Show/hide the blue 'new version' hint left of the gear button."""
+        if available:
+            self._update_hint.setText("发现新版本 v{}".format(version))
+            self._update_hint.setToolTip("点击进入设置更新")
+        self._update_hint.setVisible(bool(available))
 
     def _create_work_area(self):
         """Horizontal splitter: left material panel | canvas | right params."""
@@ -589,7 +596,15 @@ class MainWindow(QMainWindow):
                 padding: 4px 14px;
             }
             #settingsBtn:hover { color: #0078d4; background: #e8f0fb; }
-            #settingsBtn[hasUpdate="true"] { color: #c42b1c; font-weight: bold; }
+            #updateHint {
+                font-family: "Microsoft YaHei", "Segoe UI", sans-serif;
+                font-size: 12px;
+                color: #0078d4;
+                background: transparent;
+                border: none;
+                padding: 4px 8px;
+            }
+            #updateHint:hover { text-decoration: underline; }
 
             /* Work splitter */
             QSplitter#workSplitter::handle {