Improve settings page UX

[afurm]

Closes #42.

Summary

• Reworked settings into shadcn Tabs for OpenAI, Advanced, and Board flows.
• Hid board-only search, filters, and New task actions while viewing settings.
• Split save behavior by tab so board saves do not send provider patches.
• Added inline validation for advanced numeric fields and empty focus-area names.
• Tightened focus-area rows for responsive layouts and focused newly added rows automatically.

Validation

• npm run typecheck
• npm test -- --run src/client/components/SettingsView.test.tsx src/client/App.test.tsx
• npm run build
• git diff --check
• Browser smoke at desktop and 390px mobile on http://localhost:5174 for settings tabs, hidden board actions, and Add area autofocus.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Stop treating failed metadata fetches as infinite loading

When the initial onGetOpenAiAuth() and onGetOpenAiAccountInfo() calls both reject (for example during a transient backend outage), both states stay null because the Promise.allSettled handler only updates fulfilled results, so accountMetadataLoading remains true forever and the OAuth account panel never appears. In that state users lose the Connect/Refresh controls and have no in-page recovery path besides a full reload.

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