Show save/execution error dialogs on desktop #264

This commit introduces system-native error dialogs on desktop
application for code save or execution failures, addressing user confusion
described in issue #264.

This commit adds informative feedback when script execution or saving
fails.

Changes:

- Implement support for system-native error dialogs.
- Refactor `CodeRunner` and `Dialog` interfaces and their
  implementations to improve error handling and provide better type
  safety.
- Introduce structured error handling, allowing UI to display detailed
  error messages.
- Replace error throwing with an error object interface for controlled
  handling. This ensures that errors are propagated to the renderer
  process without being limited by Electron's error object
  serialization limitations as detailed in electron/electron#24427.
- Add logging for dialog actions to aid in troubleshooting.
- Rename `fileName` to `defaultFilename` in `saveFile` functions
  to clarify its purpose.
- Centralize message assertion in `LoggerStub` for consistency.
- Introduce `expectTrue` in tests for clearer boolean assertions.
- Standardize `filename` usage across the codebase.
- Enhance existing test names and organization for clarity.
- Update related documentation.

docs/desktop-vs-web-features.md

@@ -9,6 +9,8 @@ This table highlights differences between the desktop and web versions of `priva
 | [Auto-updates](#auto-updates) | 🟢 Available | 🟢 Available |
 | [Logging](#logging) | 🟢 Available | 🔴 Not available |
 | [Script execution](#script-execution) | 🟢 Available | 🔴 Not available |
+| [Error handling](#error-handling) | 🟢 Advanced | 🟡 Limited |
+| [Native dialogs](#error-handling) | 🟢 Available | 🔴 Not available |
 
 ## Feature descriptions
 
@@ -53,7 +55,7 @@ Log file locations vary by operating system:
 The desktop version of privacy.sexy enables direct script execution, providing a seamless and integrated experience.
 This direct execution capability isn't available in the web version due to inherent browser restrictions.
 
-**Logging and storage:**
+**Script execution history:**
 
 For enhanced auditability and easier troubleshooting, the desktop version keeps a record of executed scripts in designated directories.
 These locations vary based on the operating system:
@@ -62,7 +64,13 @@ These locations vary based on the operating system:
 - Linux: `$HOME/.config/privacy.sexy/runs`
 - Windows: `%APPDATA%\privacy.sexy\runs`
 
-**Native file system dialogs:**
+### Error handling
 
-The desktop version uses native system file save dialogs, offering more features and reliability compared to the browser's file system dialogs.
+The desktop version of privacy.sexy features advanced error handling capabilities.
+It employs robust and reliable execution strategies, including self-healing mechanisms, and provides guidance and troubleshooting information to resolve issues effectively.
+In contrast, the web version has more basic error handling due to browser limitations and the nature of web applications.
+
+### Native dialogs
+
+The desktop version uses native dialogs, offering more features and reliability compared to the browser's file system dialogs.
 These native dialogs provide a more integrated and user-friendly experience, aligning with the operating system's standard interface and functionalities.