feat(matugen): add standalone Spicetify theme

[hthienloc]

Adds a standalone DMS Spicetify theme generated from the current Matugen colors. Disabling the template restores the marketplace theme.

Due to a Spicetify limitation, theme changes cannot be applied on the fly and only take effect after Spotify is reloaded or restarted.

[hthienloc]

/claude review

[claude]

Claude review

Two issues; wiring itself (registry, SettingsSpec, SettingsData, Theme skip list, search index) is complete and consistent.

• User-facing template description not wrapped in I18n.tr() with context, quickshell/Modules/Settings/ThemeColorsTab.qml:2702
• disableSpicetify() unconditionally forces current_theme marketplace (and restarts Spotify), clobbering a theme the user chose themselves, quickshell/Modules/Settings/ThemeColorsTab.qml:258

Checked: template ID wiring across Go/QML, matugen config placeholder substitution and post_hook, spicetify.ini color keys, search index format vs sibling entries, and translation rules in CONTRIBUTING. Model: claude-opus-5.

[hthienloc]

/claude review

[claude]

Claude review

No issues found. Both findings from the previous review are addressed: the description is now wrapped in I18n.tr() with translator context, and the restore path saves/restores the user's prior theme and color scheme, gated on current_theme actually being DMS, with --no-restart.

Checked: template ID wiring (Go templateRegistry, SettingsSpec.js, SettingsData, Theme.qml skip lists both branches), CONFIG_DIR/SHELL_DIR substitution against substituteVars (the 'CONFIG_DIR/ quoted-prefix rule holds for the state= assignment), TOML multi-line-literal validity and shell quoting of the post_hook, the JS template literal in restoreSpicetifyTheme (no accidental ${} capture) and _configDir matching Go's XDGConfigHome(), save/restore round trip including the failure and non-DMS branches, matugen color token names and hex_stripped against sibling templates, and the search-index entry against the generator's sort order and synonym map. Model: claude-opus-5.