fix: top/bottom edge resize broken — menubar ate events + minimumSize clamped to 1121px

Two independent root causes for '左右能拉，上下不能拉':

1. Event delivery: the top 6px edge band belongs to QMenuBar, which
   actively consumes mouse events (menu hover) — nothing ever propagated
   to QMainWindow, so T/TL/TR (and maximize-restore from top edge) were
   dead on every platform. Install an event filter on menuBar()/statusBar():
   within the edge band it handles hover cursor, press (grabMouse), drag
   and release; outside the band everything passes through (menus open
   normally, native QSizeGrip corner drag preserved).

2. Layout minimum: MonitorPanel's minimumSizeHint (~1015px of stacked
   tables/group boxes) propagated through QTabWidget → central widget →
   QMainWindow, making the window minimum size 898x1121. Any vertical
   shrink was clamped dead. Set explicit per-tab-page minimumSize
   (320x200) + window minimumSize (760x480).

Tests: test_resize.py now drives edges through real event delivery
(childAt → child widget, propagation/filter path) for L/R/T/B/TL/TR/BL,
verifies BR stays on QSizeGrip, maximize-restore via menubar filter,
and minimum-size regression. All 8 suites pass.

ui/main_window.py

@@ -7,7 +7,7 @@ import sys
 import time
 from typing import Optional
 
-from PyQt5.QtCore import Qt, QSize
+from PyQt5.QtCore import Qt, QSize, QEvent
 from PyQt5.QtGui import QFont, QIcon
 from PyQt5.QtWidgets import (
     QMainWindow, QWidget, QVBoxLayout, QHBoxLayout, QListWidget, QListWidgetItem,
@@ -47,6 +47,13 @@ class MainWindow(QMainWindow):
         self._build_menu()
         self._build_statusbar()
 
+        # 菜单栏/状态栏事件过滤器：
+        # 窗口上下边缘分别被 QMenuBar / QStatusBar 覆盖，QMenuBar 会主动消费
+        # 鼠标事件（悬停高亮菜单），事件不会传播到 QMainWindow，导致上边缘
+        # （及最大化时从顶部拖还原）永远失效。装过滤器在边缘带内截获处理。
+        self.menuBar().installEventFilter(self)
+        self.statusBar().installEventFilter(self)
+
         # 左侧主机栏折叠状态
         # 注意：Ctrl+B 快捷键只由「视图」菜单项（act_toggle_sidebar）承载，
         # 不再额外建 QShortcut —— 否则一次按键触发两个绑定，会 toggle 两次等于没反应
@@ -172,6 +179,16 @@ class MainWindow(QMainWindow):
         splitter.addWidget(self.tabs)
         splitter.setSizes([280, 1000])
 
+        # 各 Tab 页显式设小最小尺寸：否则 QTabWidget 取所有页 minimumSizeHint
+        # 的最大值（MonitorPanel 内部表格/分组堆出 ~1015px 高），一路传到
+        # QMainWindow，导致窗口最小高度 > 1100px —— 上下边缘拖动被 clamp 死，
+        # 表现为"上下不能拉"。QSplitter 子件默认 minimumSize=0，压缩无碍。
+        for _page in (self.terminal_panel, self.file_browser,
+                      self.monitor, self.ai_panel):
+            _page.setMinimumSize(320, 200)
+        # 窗口级合理下限（显式 minimumSize 覆盖布局算出的巨大值）
+        self.setMinimumSize(760, 480)
+
     def _toggle_sidebar(self):
         """折叠/展开左侧主机栏"""
         self._sidebar_collapsed = not self._sidebar_collapsed
@@ -620,7 +637,7 @@ class MainWindow(QMainWindow):
             return "B"
         return ""
 
-    def _edge_to_cursor(self, edge: str):
+    def _edge_to_cursor(self, edge: str, widget=None):
         from PyQt5.QtGui import QCursor
         from PyQt5.QtCore import Qt as _Qt
         cursors = {
@@ -631,10 +648,58 @@ class MainWindow(QMainWindow):
         }
         c = cursors.get(edge)
         if c is not None:
-            self.setCursor(QCursor(c))
+            (widget or self).setCursor(QCursor(c))
 
-    def _restore_cursor(self):
-        self.unsetCursor()
+    def _restore_cursor(self, widget=None):
+        (widget or self).unsetCursor()
+
+    def eventFilter(self, obj, e):
+        """拦截菜单栏/状态栏上的鼠标事件，实现上/下边缘拖动调整窗口。
+
+        QMenuBar 主动消费鼠标事件（悬停高亮菜单项），事件不会向上传播到
+        QMainWindow，上边缘 hit-test 永远收不到事件；状态栏在部分平台/样式
+        下同理。过滤器只在 6px 边缘带内接管，其余区域原样放行
+        （菜单照常点开、QSizeGrip 原生右下角拖动不受影响）。
+        """
+        mb, sb = self.menuBar(), self.statusBar()
+        if obj is mb or obj is sb:
+            et = e.type()
+            if et == QEvent.MouseMove:
+                # 拖动中：press 时已 grabMouse，move 持续走这里
+                if self._resize_edge and (e.buttons() & Qt.LeftButton):
+                    self._do_resize(e.globalPos())
+                    return True
+                # 悬停：边缘带内显示调整光标并屏蔽菜单高亮，带外放行
+                if not e.buttons():
+                    edge = self._hit_test_edge(obj.mapTo(self, e.pos()))
+                    if edge:
+                        self._edge_to_cursor(edge, obj)
+                        return True
+                    self._restore_cursor(obj)
+                return False
+            if et == QEvent.MouseButtonPress and e.button() == Qt.LeftButton:
+                # 最大化时：菜单栏顶部边缘按下 → 还原并跟随鼠标
+                if obj is mb and self.isMaximized() and e.pos().y() <= self._resize_margin:
+                    self._restore_from_max(e.globalPos())
+                    return True
+                edge = self._hit_test_edge(obj.mapTo(self, e.pos()))
+                if edge:
+                    self._resize_edge = edge
+                    self._resize_start_geo = self.geometry()
+                    self._resize_start_pos = e.globalPos()
+                    obj.grabMouse()  # 后续 move/release 全部经过本过滤器
+                    return True
+                return False
+            if et == QEvent.MouseButtonRelease and self._resize_edge:
+                self._resize_edge = ""
+                self._resize_start_geo = None
+                self._resize_start_pos = None
+                obj.releaseMouse()
+                return True
+            if et == QEvent.Leave:
+                self._restore_cursor(obj)
+                return False
+        return super().eventFilter(obj, e)
 
     def mouseMoveEvent(self, e):
         # 拖动中