feat(frontend): follow system color scheme in settings

[xujiantop-crypto]

Summary

• Add a System option to the existing Light/Dark theme setting.
• Persist the selected preference and update the resolved theme when the operating system changes color scheme.
• Use the resolved theme for the sidebar logo, so the logo stays legible in System mode.

Refs #254. This is only the system-theme preference; the other requested Settings options remain out of scope.

Type of change

• Bug fix (fix:)
• New feature / service UI (feat:)
• Breaking change (feat!: or fix!:)
• Docs / chore

Area

• Frontend (packages/frontend)
• API / Cloud Proxy (packages/api)
• Cloud Explorer adapter / schema
• Build / CI / Docker

Verification

• pnpm lint, pnpm type-check, pnpm test, and pnpm build pass locally on main 82f2c20. The test run completed with 1,142 API tests and 32 frontend tests.
• The new Settings test covers System selection, operating-system theme changes, saved preference, and manual Light/Dark overrides.
• Browser-checked the Settings page at desktop and 390px widths. The three-option control has no horizontal overflow at 390px. Emulating a dark system theme changed the page to dark while retaining the System preference; the preference and resolved theme survived reload.
• Floci core was not running; this change does not alter resource operations.

Checklist

• pnpm lint, pnpm type-check, pnpm test, and pnpm build pass locally
• New or updated tests added where it makes sense
• No fake/mock data added
• Commit messages / PR title follow Conventional Commits

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Adds system color scheme preference to theme settings.

The PR appears safe to merge; no outstanding issue was identified.

Summary

The PR adds a System theme preference, resolves it before React loads, and keeps the sidebar logo aligned with the resolved theme. The changes since the previous review add first-paint resolution and a browser test for restored preferences.

_{Reviews (2) · Last reviewed commit: "fix(frontend): resolve system theme befo..."}