fix: template mobile-nav set-state-in-effect + lint-staged unmatched-pattern

[MarioCadenas]

What

Two small lint-correctness fixes, both surfaced while regression-testing the Biome→oxc migration (#538) by scaffolding and linting a fresh app:

1. template/client/src/App.tsx — the mobile-nav Sheet reset its open state inside a useEffect keyed on isMobile, which eslint-plugin-react-hooks v7 flags as react-hooks/set-state-in-effect. Fixed by deriving the open prop (open={mobileNavOpen && isMobile}) and dropping the effect.
2. package.json lint-staged — restore --no-errors-on-unmatched behavior (lost in the oxc migration) so commits touching only oxc-ignored files don't fail pre-commit.

Why

• App.tsx: This eslint error has been latent since the responsive-nav change (feat: improve template and component responsiveness #391) — eslint-plugin-react-hooks has been v7 (which added set-state-in-effect) since the template was created. It went unnoticed because CI never lints the template or a scaffolded app. The fix follows React's recommended pattern (compute during render instead of resetting state in an effect):

  -import { useState, useEffect } from 'react';+import { useState } from 'react';
  ...
  - // Close mobile nav when viewport crosses to desktop- useEffect(() => {- if (!isMobile) setMobileNavOpen(false);- }, [isMobile]);
  ...
  - <Sheet open={mobileNavOpen} onOpenChange={setMobileNavOpen}>+ <Sheet open={mobileNavOpen && isMobile} onOpenChange={setMobileNavOpen}>

  Behavior is preserved: on desktop the portaled Radix sheet is forced closed; on mobile the toggle works; a mobile→desktop resize closes it and Radix fires onOpenChange(false), keeping state in sync — no effect needed.

• lint-staged: oxlint/oxfmt exit non-zero on an all-ignored fileset ("No files found to lint"). The pre-oxc Biome command used --no-errors-on-unmatched; this restores that via --no-error-on-unmatched-pattern on both tools.

Verification

On a freshly scaffolded app (databricks apps init from the template):

• eslint . → 0 problems (was 1 error)
• tsc -b (server + client) → passes
• vite build → succeeds

Not fixed here (follow-up)

The root gap is that CI doesn't lint the template or a scaffolded app, so this class of error stays invisible. A CI step that scaffolds an app and runs npm run lint would catch it going forward — happy to do that separately.

[github-actions]

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📦 Try this PR's app template

Scaffolds a new app from this PR's SDK build. Run it in any folder (requires the GitHub CLI — gh auth login — and the Databricks CLI):

gh run download 32119194591 -R databricks/appkit -n appkit-template-0.61.1-pr.9fb8285-fix-template-mobile-nav-set-state-in-effect-539 -D appkit-pr-539 \
&& unzip -o "appkit-pr-539/appkit-template-0.61.1-pr.9fb8285-fix-template-mobile-nav-set-state-in-effect-539.zip" -d "appkit-pr-539" \
&& databricks apps init --template "appkit-pr-539"

The template pins @databricks/appkit and @databricks/appkit-ui to tarballs built from this branch, so the scaffolded app runs against this PR's code.

[pkosiec]

LGTM