[Feature] Solarized themes + follow OS light/dark preference + more light variants

Summary

The dashboard supports seven themes but only one is light (vanilla), and theme selection ignores the OS prefers-color-scheme. Users on systems that auto-switch between light and dark mode can't have the dashboard follow along, and a popular palette (Solarized) is missing entirely.

Current state

• interface/src/hooks/useTheme.ts defines default | vanilla | midnight | noir | slate | nord | mocha | catpucchino
• Of those, only vanilla is light
• No prefers-color-scheme listener anywhere in interface/ (verified by grep)
• Tokens come from @spacedrive/tokens@0.2.3 — its themes/ directory has dark.css, light.css, midnight.css, mocha.css, noir.css, nord.css, slate.css (no Solarized)
• Theme is persisted under localStorage["spacebot-theme"] as a single id

Proposed change

1. Add solarized-light and solarized-dark theme tokens. Either upstream in @spacedrive/tokens (preferred — keeps the same tokenization model the rest of the dashboard uses) or as a local override stylesheet imported in interface/src/styles.css.
2. Add 1-2 more light variants (e.g. paper, or Catppuccin latte to pair with the existing mocha).
3. Add a "mode" selector alongside the theme picker in Settings: light | dark | system.
   • When system, watch window.matchMedia("(prefers-color-scheme: dark)") and swap between a chosen light theme and a chosen dark theme.
   • Persist mode + per-mode theme choices separately (e.g. spacebot-theme-mode, spacebot-theme-light, spacebot-theme-dark).
4. Settings UI: when mode is system, render two pickers ("Light theme" + "Dark theme") instead of one.

Out of scope

• Custom user-authored themes (separate issue)
• Per-component theme overrides

Open questions

• Is the maintainer happy to take Solarized as a local override here, or should the addition go upstream to @spacedrive/tokens? Upstream is cleaner long-term but slower to land.

Start with interface/src/hooks/useTheme.ts to understand the existing theme IDs and persistence, then inspect interface/src/styles.css and the Settings theme picker. Resolve whether Solarized belongs in @spacedrive/tokens or a local stylesheet before implementing mode and per-mode theme choices. Done means light, dark, and system modes work, system mode responds to prefers-color-scheme, and the selected choices persist.