feat(skin-studio): desktop theme editor plugin

[weiweiplus0527]

What

A full-featured Hermes Desktop theme editor — the most complete theme plugin in this repo, as a deep Chinese localization of Theme Forge (MIT, by @criptogus), which itself is an open PR here.

skin-studio ships as a desktop plugin (plugin.js, pure ESM) + an optional Python backend (dashboard/plugin_api.py) that applies themes through the canonical skin path: writes $HERMES_HOME/skins/<name>.yaml + sets display.skin, so the gateway's skin watcher broadcasts skin.changed and every surface (desktop/CLI/TUI) repaints in ~1s with no restart.

What it does that Hermes can't natively

Feature	Why it doesn't exist natively
Wallpaper / animated video backdrop + overlay/blur	DesktopTheme model only supports solid colors
Extended palette — --ui-red/green/blue/purple/yellow/cyan/orange/warm	Those colors are fixed in the app's styles.css
Text bold levels, chat font size, markdown accent colors	Not configurable
Matrix-style digit wall / hanzi rain / CRT scanlines	Impossible in the theme model
One-click apply	The desktop doesn't expose setTheme to plugins

Highlights beyond Theme Forge

• 15 preset themes — 6 Chinese-style (水墨/青花瓷/故宫/竹林/敦煌/汉字雨), 4 anime-style (EVA/高达/初音/鬼灭), 5 classics
• Global FX layer (new architecture): rain effects are decoupled from color themes — pick any theme, overlay any FX (follow-theme / none / digit wall / hanzi rain), with global font-size & speed sliders. CRT scanlines get a three-state switch and are mutually exclusive with the digit wall.
• Digit wall (user-requested redesign of matrix rain): full-screen 0–9 grid that refreshes in place — no falling, no stacking, dim phosphor green so it never fights with text
• Auto-color from image: median-cut palette extraction + WCAG contrast guarantees (4.5:1 fg/bg, 3:1 muted) + 10 palette templates
• Video media library: large local videos in IndexedDB (GB-scale), survive restarts, click-to-apply
• Fully Chinese UI (the plugin is a localization product for zh users)

Testing

1. cp -R skin-studio ~/.hermes/desktop-plugins/ + cp -R skin-studio ~/.hermes/plugins/ (backend under plugins/skin-studio/dashboard/), enable skin-studio in plugins.enabled (YAML list)
2. Restart the Desktop app (backend routes mount at startup), open 皮肤工坊 from the sidebar
3. Tune colors/background/text, pick a global FX, click 应用 — the whole desktop repaints

License

MIT. Retains the Theme Forge copyright line (fork) plus a Skin Studio line. Film/anime presets are palette homages with no official affiliation.