feat: tmux 多 pane 分屏（pane-per-surface + refresh-client -C 尺寸协调）

- TmuxController 重构为 pane-per-surface：TmuxPaneSurface(session+state+gate/pane)
  + TmuxWindow(panes 字典/visibleLayout 渲染/fullLayout diff) + surfaceByPane O(1) 路由
- 尺寸走路线 b：attach 发 refresh-client -C WxH 让 tmux 布局，pane surface 尺寸取 layout
  rect（%output 按 tmux pane 宽高排版，一致才不换行/清屏错乱）；surface resize 只断言不反向驱动
- applyLayout reconcile(增删留、复用不重建)；新 pane capture-pane %end 前丢弃 %output
- 输入绑 pane→send-keys -t %self；tap→select-pane；ContentView 按 rect 绝对定位分屏 + 焦点边框
- 前置修复：tmux 网关字节改 TmuxByteChannel(AsyncStream 单消费者)保序，防多 pane 打碎协议
- 验证(192.168.9.199 直连 tmux -CC attach)：左右 pane 各渲染 LEFT/RIGHT 输出、实时、无错乱

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/TerminalX/iOS/ContentView.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 import GhosttyTerminal
+import TXCore
 
 struct ContentView: View {
     @StateObject private var model = SSHTerminalModel()
@@ -162,19 +163,75 @@ struct TmuxTabChip: View {
     }
 }
 
+/// 一个 window：按 tmux 可见布局树把多 pane 绝对定位为分屏（每 pane 一 surface）。
 struct TmuxWindowView: View {
     @ObservedObject var window: TmuxWindow
     let controller: TmuxController
+
+    var body: some View {
+        GeometryReader { geo in
+            if let layout = window.visibleLayout {
+                let root = layout.root.rect
+                let cw = geo.size.width / CGFloat(max(1, root.width))
+                let ch = geo.size.height / CGFloat(max(1, root.height))
+                ZStack(alignment: .topLeading) {
+                    ForEach(leaves(layout.root), id: \.pane.raw) { item in
+                        if let surface = window.panes[item.pane] {
+                            TmuxPaneView(
+                                surface: surface,
+                                isActive: window.activePane == item.pane,
+                                onTap: { controller.selectPane(item.pane, in: window.id) },
+                                onReady: { controller.markPaneReady(item.pane) }
+                            )
+                            .frame(width: CGFloat(item.rect.width) * cw,
+                                   height: CGFloat(item.rect.height) * ch)
+                            .position(x: (CGFloat(item.rect.x) + CGFloat(item.rect.width) / 2) * cw,
+                                      y: (CGFloat(item.rect.y) + CGFloat(item.rect.height) / 2) * ch)
+                        }
+                    }
+                }
+            } else {
+                Color.clear
+            }
+        }
+    }
+
+    /// 收集布局树叶子（pane + 绝对 rect），identity 只用 paneID → 布局变化不重建 surface view。
+    private func leaves(_ node: TmuxLayout.Node) -> [(pane: TmuxPaneID, rect: TmuxLayout.Rect)] {
+        switch node {
+        case .leaf(let p, let r): return [(p, r)]
+        case .horizontal(let cs, _), .vertical(let cs, _): return cs.flatMap(leaves)
+        }
+    }
+}
+
+/// 单个 pane 的终端面 + 焦点边框 + 点击选中。
+struct TmuxPaneView: View {
+    @ObservedObject var surface: TmuxPaneSurface
+    let isActive: Bool
+    let onTap: () -> Void
+    let onReady: () -> Void
     @FocusState private var focused: Bool
 
     var body: some View {
-        TerminalSurfaceView(context: window.state)
+        TerminalSurfaceView(context: surface.state)
             .terminalFocusOnAppear($focused)
+            .overlay(
+                Rectangle().stroke(isActive ? Color.accentColor : Color.gray.opacity(0.35),
+                                   lineWidth: isActive ? 2 : 0.5)
+            )
+            // 非活动 pane 叠透明 tap-catcher（TerminalSurfaceView 会吞触摸）；活动 pane 直通终端。
+            .overlay {
+                if !isActive {
+                    Color.black.opacity(0.04).contentShape(Rectangle()).onTapGesture { onTap() }
+                }
+            }
+            .onChange(of: isActive) { _, active in focused = active }
             .task {
-                for _ in 0 ..< 300 where window.state.surfaceSize == nil {
+                for _ in 0 ..< 300 where surface.state.surfaceSize == nil {
                     try? await Task.sleep(nanoseconds: 30_000_000)
                 }
-                controller.markWindowReady(window.id)
+                onReady()
             }
     }
 }