fix(macos): fix split view layout so panels are visible and VoiceOver-reachable

The main window's NSSplitView panels (channel list, user list, chat,
activity log) were collapsing to zero size because:

1. The scroll views inside the split views were missing
   translatesAutoresizingMaskIntoConstraints = false, so Auto Layout
   couldn't manage their sizes.
2. The inner split views were also missing it.
3. The voice panel had no height constraint, so it expanded to fill
   all available space (539px of the 600px window), starving the
   outer split view down to 1px tall.
4. The split views had no initial divider positions, so panels
   collapsed to zero even when the split view had space.

Add translatesAutoresizingMaskIntoConstraints = false to all four
scroll views and both inner split views, give the voice panel a
96px height constraint, and set initial divider positions after the
window is on screen. The panels now get reasonable space, are
visible on screen, and are reachable by VoiceOver.

clients/apple/macOS/VoiceCatMac/Windows/MainWindowController.swift

@@ -125,6 +125,7 @@ final class MainWindowController: NSWindowController, NSWindowDelegate {
         let innerSplit = NSSplitView()
         innerSplit.isVertical = false
         innerSplit.dividerStyle = .thin
+        innerSplit.translatesAutoresizingMaskIntoConstraints = false
 
         let channelPanel = buildChannelPanel()
         let userPanel = buildUserPanel()
@@ -137,6 +138,7 @@ final class MainWindowController: NSWindowController, NSWindowDelegate {
         let rightSplit = NSSplitView()
         rightSplit.isVertical = false
         rightSplit.dividerStyle = .thin
+        rightSplit.translatesAutoresizingMaskIntoConstraints = false
         let chatPanel = buildChatPanel()
         let activityPanel = buildActivityPanel()
         rightSplit.addArrangedSubview(chatPanel)
@@ -178,6 +180,17 @@ final class MainWindowController: NSWindowController, NSWindowDelegate {
             composeBar.bottomAnchor.constraint(equalTo: contentView.bottomAnchor),
             composeBar.heightAnchor.constraint(equalToConstant: 36),
         ])
+
+        // Set initial divider positions so panels get reasonable space instead of
+        // collapsing to zero. These are applied after the window is on screen.
+        DispatchQueue.main.async { [weak self, weak outerSplit, weak innerSplit, weak rightSplit] in
+            // outerSplit is vertical (left|right): divide at 40% from left
+            outerSplit?.setPosition(360, ofDividerAt: 0)
+            // innerSplit is horizontal (channels on top, users below): divide at 60% from top
+            innerSplit?.setPosition(260, ofDividerAt: 0)
+            // rightSplit is horizontal (chat on top, activity below): divide at 70% from top
+            rightSplit?.setPosition(280, ofDividerAt: 0)
+        }
     }
 
     private func buildChannelPanel() -> NSView {
@@ -195,6 +208,7 @@ final class MainWindowController: NSWindowController, NSWindowDelegate {
         sv.documentView = channelOutlineView
         sv.hasVerticalScroller = true
         sv.borderType = .noBorder
+        sv.translatesAutoresizingMaskIntoConstraints = false
 
         let menu = NSMenu()
         menu.delegate = self
@@ -221,6 +235,7 @@ final class MainWindowController: NSWindowController, NSWindowDelegate {
         sv.documentView = userTableView
         sv.hasVerticalScroller = true
         sv.borderType = .noBorder
+        sv.translatesAutoresizingMaskIntoConstraints = false
         return sv
     }
 
@@ -233,6 +248,7 @@ final class MainWindowController: NSWindowController, NSWindowDelegate {
         sv.documentView = chatTextView
         sv.hasVerticalScroller = true
         sv.borderType = .noBorder
+        sv.translatesAutoresizingMaskIntoConstraints = false
         return sv
     }
 
@@ -248,6 +264,7 @@ final class MainWindowController: NSWindowController, NSWindowDelegate {
         sv.documentView = activityTableView
         sv.hasVerticalScroller = true
         sv.borderType = .noBorder
+        sv.translatesAutoresizingMaskIntoConstraints = false
         return sv
     }
 
@@ -365,6 +382,8 @@ final class MainWindowController: NSWindowController, NSWindowDelegate {
 
             levelMeter.widthAnchor.constraint(equalToConstant: 100),
             devicePicker.widthAnchor.constraint(greaterThanOrEqualToConstant: 160),
+
+            panel.heightAnchor.constraint(equalToConstant: 96),
         ])
         return panel
     }