feat: rest-to-reveal hint for dock separators

Separators stay invisible until the mouse rests on one for ~1s (or a
drag starts); the QSS ::separator:hover rule does the hit-testing and a
dynamic separatorHint property gates it, so event() never needs to know
where separators are.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/aare/gui/main_window.py

@@ -87,6 +87,7 @@ from aare.gui.styles import (
     APP_BACKGROUND,
     DARK_TEXT,
     DOCK_CONTENT_LEFT_PAD,
+    SEPARATOR_HINT_DELAY_MS,
     THEME_FADE_MS,
     THEME_ORIGINAL,
     THEME_PORTRAIT,
@@ -251,6 +252,16 @@ class MainWindow(QMainWindow):
 
         self.setStyleSheet(f"background-color: {APP_BACKGROUND};")
 
+        # Resize-line hint (see SEPARATOR_HINT in styles.py): WA_Hover gives
+        # us HoverMove without a button held; the single-shot timer implements
+        # the "rested for 1s" gate. The QSS ::separator:hover rule does the
+        # hit-testing, so event() never needs to know where separators are.
+        self.setAttribute(Qt.WidgetAttribute.WA_Hover, True)
+        self._separator_hint_timer = QTimer(self)
+        self._separator_hint_timer.setSingleShot(True)
+        self._separator_hint_timer.setInterval(SEPARATOR_HINT_DELAY_MS)
+        self._separator_hint_timer.timeout.connect(lambda: self._set_separator_hint(True))
+
         root_widget = QWidget(parent=self)
         root_widget.setObjectName("mainContentRoot")
         root_layout = QVBoxLayout(root_widget)
@@ -2871,6 +2882,38 @@ class MainWindow(QMainWindow):
         if dx or dy:
             dock.move(geo.x() + dx, geo.y() + dy)
 
+    def _set_separator_hint(self, on: bool) -> None:
+        if self.property("separatorHint") == on:
+            return
+        self.setProperty("separatorHint", on)
+        # Property selectors are only re-evaluated on repolish.
+        self.style().unpolish(self)
+        self.style().polish(self)
+        self.update()
+
+    def event(self, event):
+        # Separator press/drag never reaches mousePressEvent — QMainWindow
+        # eats it inside event() to start the separator move — so the hint
+        # gate must sit here, before super() dispatches.
+        t = event.type()
+        if t in (QEvent.Type.HoverEnter, QEvent.Type.HoverMove):
+            # Any move restarts the 1s countdown ("hover and rest"); during a
+            # drag (button held) the hint stays on instead.
+            if QApplication.mouseButtons() == Qt.MouseButton.NoButton:
+                self._set_separator_hint(False)
+                self._separator_hint_timer.start()
+        elif t == QEvent.Type.HoverLeave:
+            self._separator_hint_timer.stop()
+            self._set_separator_hint(False)
+        elif t == QEvent.Type.MouseButtonPress:
+            # Press shows the line immediately, no 1s wait.
+            self._separator_hint_timer.stop()
+            self._set_separator_hint(True)
+        elif t == QEvent.Type.MouseButtonRelease:
+            self._set_separator_hint(False)
+            self._separator_hint_timer.start()
+        return super().event(event)
+
     def eventFilter(self, obj, event):
         # Closing a floated (popped-out) dock re-docks it instead of hiding —
         # otherwise the panel silently disappears and has to be restored via

src/aare/gui/styles.py

@@ -98,6 +98,7 @@ DOCK_CONTENT_LEFT_PAD = 10
 # separator under the cursor fills with SEPARATOR_HINT. The rest/drag gate
 # lives in MainWindow.event(); the QSS :hover part picks the one separator.
 SEPARATOR_HINT = "rgba(168, 178, 192, 50%)"  # scrollbar-track grey @50%
+SEPARATOR_HINT_DELAY_MS = 888  # int, used in code, not QSS
 
 # Theme-switch screenshot cross-fade duration (int ms, used in code).
 THEME_FADE_MS = 250