feat(theme): support system light and dark themes

[Soundcreates]

Summary

• add persisted light and dark theme mappings
• add optional Follow system appearance mode using prefers-color-scheme
• expose filtered light/dark theme pickers in Appearance settings
• preserve SQL editor Same as App synchronization

Closes #649

Validation

• pnpm typecheck
• pnpm lint
• pnpm build
• cargo check --manifest-path src-tauri/Cargo.toml
• git diff --check

The repository-wide cargo fmt --check currently reports unrelated pre-existing formatting differences outside this change.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• src-tauri/src/config.rs
• src/components/settings/AppearanceTab.tsx
• src/contexts/ThemeProvider.tsx
• src/i18n/locales/en.json

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The change adds persisted followSystemTheme, lightThemeId, and darkThemeId config fields with correct Rust Option-guarded merging in save_config, mirrors them through the AppConfig TS interface, wires the new pickers in AppearanceTab, and updates the ThemeProvider load/save/system-listener effects consistently. Defaults are applied correctly via DEFAULT_THEME_SETTINGS, the system matchMedia listener uses the configured light/dark IDs, and effect dependencies cover the read state with no stale-closure gaps. No security, runtime, or logic defects found in the changed lines.

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_{Reviewed by glm-5.2 · Input: 27.7K · Output: 6.5K · Cached: 224.8K}