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/InteractiveTerminalViewModelTests.cs

@@ -124,4 +124,35 @@ public class InteractiveTerminalViewModelTests
         terminal.IsRunning = true; // records LaunchedAt via the first clock call
         return terminal;
     }
+
+    // ── Paste/drop failure reporting (fix: PasteAsync used to swallow every exception and return
+    //    void, so a failed Ctrl+V or file drop gave the user no signal at all) ────────────────────
+
+    [Fact]
+    public async Task PasteAsync_ReturnsFalse_WhenSessionNotRunning()
+    {
+        using var terminal = new InteractiveTerminalViewModel();
+
+        Assert.False(await terminal.PasteAsync());
+    }
+
+    [Fact]
+    public async Task SendTextAsync_ReturnsFalse_WhenSessionNotRunning()
+    {
+        using var terminal = new InteractiveTerminalViewModel();
+
+        Assert.False(await terminal.SendTextAsync("dropped/path"));
+    }
+
+    [Fact]
+    public void ReportSendFailed_RaisesErrorReported()
+    {
+        using var terminal = new InteractiveTerminalViewModel();
+        string? error = null;
+        terminal.ErrorReported += msg => error = msg;
+
+        terminal.ReportSendFailed();
+
+        Assert.NotNull(error);
+    }
 }