[codex] Tighten host tree topbar UX

[binaricat]

Summary

• Add separate Custom CSS hooks for the host-list toggle and quick-switcher plus button in the top tab bar.
• Stop automatically reopening the host tree sidebar when returning to terminal/editor work tabs.
• Align the Vault surface to the top tab bar by removing the extra top padding.

Validation

• node --test --import tsx application/app/AppHostTreeLayer.test.ts components/TopTabs.test.ts components/VaultViewLayout.test.ts
• npm run lint
• npm run build
• npm test passed before the final quick-switcher hook addition; the focused tests, lint, and build were rerun after that change.
• Opened http://127.0.0.1:5173/ in the in-app browser and verified the Vault surface starts immediately below the top tab bar. Terminal creation cannot be fully exercised in browser-only Vite mode because the Electron terminal backend is unavailable there.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Cover the overflow quick switcher toggle

When the tab strip overflows, the !hasOverflow plus button is not rendered and the quick switcher is instead opened by the overflow MoreHorizontal button below, which does not have this data-section. As a result, custom CSS using the newly documented [data-section="top-tabs-quick-switcher-toggle"] hook only hides/styles the quick-switcher control until enough tabs are open, at which point the same control reappears as the overflow button. Add the same hook to the overflow quick-switcher button or a shared wrapper.

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