Build litmus extract-colors command (litmus-z20l)

Add an extract-colors subcommand to litmus-capture (or a new litmus-extract crate):

• Reads ThemeDefinition files from themes/
• For each provider mapping, looks up the theme name in vendored data (vendor/kitty-themes/, vendor/wezterm-colorschemes/)
• Parses the provider’s native format into ProviderColors (reuse/extend existing kitty.rs parser, add wezterm TOML parser)
• Writes {theme-slug}.{provider}.toml next to the definition file
• Flags: –provider (filter to one provider), –theme (filter to one theme)
• Skips if generated file already exists and vendored source hasn’t changed (optional optimization)

Depends on: new model types, vendored theme data

Plan

Step 1: Add wezterm TOML parser to litmus-model

New wezterm.rs module with parse_wezterm_scheme() → Theme Format: uses ansi/brights arrays, cursor_bg/cursor_fg, selection_bg/selection_fg

Step 2: Add Theme → ProviderColors conversion

Helper in provider module: ProviderColors::from_theme(theme, provider_slug, version)

Step 3: Add ProviderColors serialization to TOML

ProviderColors::to_toml() → formatted output matching expected generated file format

Step 4: Add ExtractColors subcommand to litmus-capture

• Read ThemeDefinition files from themes/
• For each provider mapping, look up vendored theme file
• Parse with appropriate parser → Theme → ProviderColors
• Write {slug}.{provider}.toml
• Flags: –provider, –theme

Step 5: Add kitty vendor lookup

Look up theme name in vendor/kitty-themes/themes.json index → find .conf file

Step 6: Add wezterm vendor lookup

Look up theme name in vendored .toml files (scan by metadata.name field)

Summary of Changes

Implemented the extract-colors pipeline across two crates:

litmus-model additions:

• wezterm.rs: New parser for wezterm color scheme TOML format (ansi/brights arrays, optional cursor/selection)
• provider.rs: Added ProviderColors::from_theme() conversion and to_toml() serialization

litmus-capture additions:

• extract.rs: Vendor index builders (kitty themes.json, wezterm metadata.name + aliases), theme definition scanner, provider-specific color extraction
• main.rs: New ExtractColors subcommand with –provider, –theme, –force flags

End-to-end tested: successfully extracts colors from both kitty and wezterm vendor data, writing correctly formatted ProviderColors TOML files.