[FEATURE] Web Json Generator

[Skeptic-systems]

Feature Description

Add a web-based JSON Theme Generator that lets users create theme JSONs easily and export them for import in the desktop app via inject-custom-themes.

Problem Statement

Writing theme JSON by hand is error-prone and too technical, leading to invalid JSON and failed imports.

Proposed Solution

• Web UI to edit theme fields (based on the theme schema)
• Live validation + clear error messages
• Export: Download + Copy to clipboard
• Import an existing theme JSON to edit and re-export (round-trip)

Acceptance Criteria

• Generated JSON is valid and compatible with inject-custom-themes
• Live validation prevents common mistakes
• Export works via download and copy
• Existing theme JSON can be imported, edited, and re-exported