When theme is set to 'auto', checking theme === 'dark' returns false even
when the system preference is dark mode. This caused charts and custom
styles to use light mode colors in a dark UI.
Fixed by using resolvedTheme which correctly resolves to 'light' or 'dark'
based on system preference when in auto mode.
Fixes the issue reported in PR #29 review.
- Add useModelsStore with 30s cache for model list to reduce API calls
- Refactor SystemPage to use cached models from store
- Shorten ConfigPage search placeholder to prevent text truncation
