fix: Add retry logic for Enter key send in NudgeSession/NudgePane (#53)

When sending messages to Claude sessions via tmux, the Enter key send
could fail silently. This caused polecats to receive their initial
prompt but never submit it - the message appeared in Claude's input
area but Enter was never pressed.

Add retry logic (up to 3 attempts with 200ms delays) for the Enter
send step in both NudgeSession() and NudgePane(). This ensures message
submission is more reliable even if tmux has transient issues.

Fixes #41

internal/tmux/tmux.go

@@ -274,12 +274,19 @@ func (t *Tmux) NudgeSession(session, message string) error {
 	// 2. Wait 500ms for paste to complete (tested, required)
 	time.Sleep(500 * time.Millisecond)
 
-	// 3. Send Enter as separate command (key to reliability)
-	if _, err := t.run("send-keys", "-t", session, "Enter"); err != nil {
-		return err
+	// 3. Send Enter with retry (critical for message submission)
+	var lastErr error
+	for attempt := 0; attempt < 3; attempt++ {
+		if attempt > 0 {
+			time.Sleep(200 * time.Millisecond)
+		}
+		if _, err := t.run("send-keys", "-t", session, "Enter"); err != nil {
+			lastErr = err
+			continue
+		}
+		return nil
 	}
-
-	return nil
+	return fmt.Errorf("failed to send Enter after 3 attempts: %w", lastErr)
 }
 
 // NudgePane sends a message to a specific pane reliably.
@@ -293,12 +300,19 @@ func (t *Tmux) NudgePane(pane, message string) error {
 	// 2. Wait 500ms for paste to complete (tested, required)
 	time.Sleep(500 * time.Millisecond)
 
-	// 3. Send Enter as separate command (key to reliability)
-	if _, err := t.run("send-keys", "-t", pane, "Enter"); err != nil {
-		return err
+	// 3. Send Enter with retry (critical for message submission)
+	var lastErr error
+	for attempt := 0; attempt < 3; attempt++ {
+		if attempt > 0 {
+			time.Sleep(200 * time.Millisecond)
+		}
+		if _, err := t.run("send-keys", "-t", pane, "Enter"); err != nil {
+			lastErr = err
+			continue
+		}
+		return nil
 	}
-
-	return nil
+	return fmt.Errorf("failed to send Enter after 3 attempts: %w", lastErr)
 }
 
 // AcceptBypassPermissionsWarning dismisses the Claude Code bypass permissions warning dialog.