feat: detect prompt-too-long errors and offer compact action

Closes #158

- Detect "Prompt is too long" in assistant text blocks in wsl_bridge
- Emit error line type instead of assistant for better visibility
- Emit compact-prompt event after the error line
- Render a compact-prompt line as an action button in the terminal
- Clicking the button sends /compact to the active session
- Add getLineClass/getLinePrefix tests for compact-prompt type

src-tauri/src/wsl_bridge.rs

@@ -1082,17 +1082,37 @@ fn process_json_line(
                             stats.write().increment_code_blocks();
                         }
 
+                        let is_prompt_too_long = text.starts_with("Prompt is too long");
+
                         let _ = app.emit(
                             "claude:output",
                             OutputEvent {
-                                line_type: "assistant".to_string(),
+                                line_type: if is_prompt_too_long {
+                                    "error".to_string()
+                                } else {
+                                    "assistant".to_string()
+                                },
                                 content: text.clone(),
                                 tool_name: None,
                                 conversation_id: conversation_id.clone(),
-                                cost: message_cost.clone(), // Include cost with assistant text
+                                cost: message_cost.clone(),
                                 parent_tool_use_id: parent_tool_use_id.clone(),
                             },
                         );
+
+                        if is_prompt_too_long {
+                            let _ = app.emit(
+                                "claude:output",
+                                OutputEvent {
+                                    line_type: "compact-prompt".to_string(),
+                                    content: String::new(),
+                                    tool_name: None,
+                                    conversation_id: conversation_id.clone(),
+                                    cost: None,
+                                    parent_tool_use_id: None,
+                                },
+                            );
+                        }
                     }
                     ContentBlock::Thinking { thinking } => {
                         state = CharacterState::Thinking;