feat: add color theme setting with light and auto modes

[johnnybakucz]

• Add workspace-scoped theme setting (dark/light/auto, default auto)
• Ship dark + light palettes in src/tui/theme.ts; colors is now a mutable object so all views re-read the active palette
• Auto mode probes the terminal via OSC 11 and falls back to COLORFGBG, then dark, if the terminal doesn't respond in 100ms
• Wire the setting into the TUI config screen (hot-applies on save) and the CLI: 'leetcode config --theme <dark|light|auto>' plus the interactive prompt

[github-actions]

Thanks for the PR, @johnnybakucz! 🎉

Before this gets reviewed, please make sure the following are checked:

• Tests pass locally (npm test)
• Type check passes (npm run typecheck)
• Lint passes (npm run lint)
• New features include tests
• Documentation updated if needed
• PR targets the dev branch (not main)

See CONTRIBUTING.md for full guidelines.

The CI pipeline will also run build, test, lint, and typecheck automatically.

[johnnybakucz]

Checklist status:

• Tests pass locally (npm test) — 280 passed, 53 skipped (2 pre-existing failures unrelated to this PR: integration tests that require npm run build state)
• Type check passes (npm run typecheck)
• Lint passes (npm run lint) — 0 errors, 31 pre-existing warnings
• New features include tests — none added; happy to add coverage for normalizeThemeInput, parseOsc11, and resolveTheme if desired
• Documentation updated if needed — README not updated yet; can add a short section under Configuration if the theme is worth documenting there
• PR targets the dev branch — retargeted from main to dev

[johnnybakucz]

Updated:

• New features include tests — added src/__tests__/tui/theme.test.ts covering normalizeThemeInput, resolveTheme (dark/light/auto + COLORFGBG detection), and applyTheme palette swap
• Documentation updated — README Configuration section now documents --theme and how auto detection works

[night-slayer18]

Thanks for the contribution!
I have verified the changes 👍🏼