fix(macos): sane chat window placement

apps/macos/Sources/Clawdis/WindowPlacement.swift

@@ -0,0 +1,54 @@
+import AppKit
+
+@MainActor
+enum WindowPlacement {
+    static func centeredFrame(size: NSSize, on screen: NSScreen? = NSScreen.main) -> NSRect {
+        let bounds = (screen?.visibleFrame ?? NSScreen.screens.first?.visibleFrame ?? .zero)
+        if bounds == .zero {
+            return NSRect(origin: .zero, size: size)
+        }
+
+        let clampedWidth = min(size.width, bounds.width)
+        let clampedHeight = min(size.height, bounds.height)
+
+        let x = round(bounds.minX + (bounds.width - clampedWidth) / 2)
+        let y = round(bounds.minY + (bounds.height - clampedHeight) / 2)
+        return NSRect(x: x, y: y, width: clampedWidth, height: clampedHeight)
+    }
+
+    static func topRightFrame(
+        size: NSSize,
+        padding: CGFloat,
+        on screen: NSScreen? = NSScreen.main) -> NSRect
+    {
+        let bounds = (screen?.visibleFrame ?? NSScreen.screens.first?.visibleFrame ?? .zero)
+        if bounds == .zero {
+            return NSRect(origin: .zero, size: size)
+        }
+
+        let clampedWidth = min(size.width, bounds.width)
+        let clampedHeight = min(size.height, bounds.height)
+
+        let x = round(bounds.maxX - clampedWidth - padding)
+        let y = round(bounds.maxY - clampedHeight - padding)
+        return NSRect(x: x, y: y, width: clampedWidth, height: clampedHeight)
+    }
+
+    static func ensureOnScreen(
+        window: NSWindow,
+        defaultSize: NSSize,
+        fallback: ((NSScreen?) -> NSRect)? = nil)
+    {
+        let frame = window.frame
+        let targetScreens = NSScreen.screens.isEmpty ? [NSScreen.main].compactMap { $0 } : NSScreen.screens
+        let isVisibleSomewhere = targetScreens.contains { screen in
+            frame.intersects(screen.visibleFrame.insetBy(dx: 12, dy: 12))
+        }
+
+        if isVisibleSomewhere { return }
+
+        let screen = NSScreen.main ?? targetScreens.first
+        let next = fallback?(screen) ?? centeredFrame(size: defaultSize, on: screen)
+        window.setFrame(next, display: false)
+    }
+}