fix(ui): report failed paste/drop in the interactive terminal

PasteAsync silently swallowed every exception and returned void, so a
package update renaming Iciclecreek's private write seam would break
Ctrl+V/drop with zero user-visible signal. PasteAsync/SendTextAsync now
return bool (mirroring SendLineAsync), and the view checks the result,
routing a failure through InteractiveTerminalViewModel.ErrorReported ->
ConPtyPaneViewModel.ErrorReported -> the existing footer error strip.

tests/ClaudeDo.Ui.Tests/ViewModels/MissionControl/ConPtyPaneViewModelTests.cs

@@ -219,6 +219,35 @@ public class ConPtyPaneViewModelTests
         Assert.True(raised);
     }
 
+    // ── Terminal.ErrorReported forwarding (fix: a failed paste/drop had no path to the footer
+    //    error strip) ────────────────────────────────────────────────────────────────────────────
+
+    [Fact]
+    public void TerminalErrorReported_Forwards_ToPaneErrorReported()
+    {
+        using var pane = NewTaskPane(NeverCompletes);
+        string? error = null;
+        pane.ErrorReported += msg => error = msg;
+
+        pane.Terminal.ReportSendFailed();
+
+        Assert.NotNull(error);
+    }
+
+    [Fact]
+    public void TerminalErrorReported_StillWiredAfterRetry()
+    {
+        using var pane = NewTaskPane(() => Failing());
+        pane.Start();
+        pane.RetryCommand.Execute(null);
+        string? error = null;
+        pane.ErrorReported += msg => error = msg;
+
+        pane.Terminal.ReportSendFailed();
+
+        Assert.NotNull(error);
+    }
+
     private static void SetRunning(ConPtyPaneViewModel pane) => pane.Terminal.IsRunning = true;
 
     // Drives the terminal past its startup grace window, then kills it: IsRunning stamps the launch