ShellDocsOptions.Theme and shelldocs init --theme do nothing #44

Summary

ShellDocsOptions.Theme (Shadcn, Fuma, Nextra) and shelldocs init --theme exist, and init prints the chosen theme in its summary, but nothing reads the value: every site gets the same palette.

Expected

Either the presets change the palette (tokens in ShellDocs.Tokens), or the option and flag are removed or clearly marked as reserved, so users don't expect a change.

Where

• src/ShellDocs.Components/ShellDocsOptions.cs (Theme, ShellDocsTheme)
• src/ShellDocs.CLI/Commands/InitCommand.cs (--theme, summary row)
• docs/TOKENS.md for how a preset would be defined