v2.3.1: add 'Re-run Onboarding' button to Help dialog

v2.3.0 had show_onboarding() method but no UI entry point. Existing
users couldn't reach the wizard since auto-migration marks them done.
Now Help dialog (F1) has a button to re-trigger the wizard.

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

ui/help_view.py

@@ -51,16 +51,29 @@ class HelpView(QDialog):
 
         button_layout = QHBoxLayout()
         button_layout.setContentsMargins(20, 10, 20, 20)
+
+        # 온보딩 다시 보기 (왼쪽)
+        onboarding_button = QPushButton("🚀 온보딩 다시 보기")
+        onboarding_button.setMinimumHeight(40)
+        onboarding_button.clicked.connect(self._reopen_onboarding)
+        button_layout.addWidget(onboarding_button)
+
         button_layout.addStretch()
+
         close_button = QPushButton(tr('btn.close'))
         close_button.setObjectName("btn_primary")
         close_button.setMinimumHeight(40)
         close_button.setMinimumWidth(120)
         close_button.clicked.connect(self.close)
         button_layout.addWidget(close_button)
-        button_layout.addStretch()
         main_layout.addLayout(button_layout)
 
+    def _reopen_onboarding(self):
+        """부모 윈도우의 show_onboarding 호출 후 도움말 닫음."""
+        self.close()
+        if self.parent() and hasattr(self.parent(), 'show_onboarding'):
+            self.parent().show_onboarding()
+
         self.setLayout(main_layout)
 
     def _make_tab(self, html: str) -> QWidget: