fix(app): reset settings scroll on category changes

[murongg]

Summary

• Reset the shared settings content scroll container whenever the active settings category changes.
• Add regression coverage for switching from a scrolled AI settings panel into Providers.

Why

• The Providers panel uses the same outer settings scroll container as other tabs but switches it to overflow-hidden.
• If a previous tab leaves a non-zero scroll offset, WebView can render the Providers panel clipped upward, matching [Bug]: 进入设置后，如果按从上到下顺序切到 供应商 tab，高概率触发显示bug #313.

Validation

• pnpm --filter @markra/app test -- SettingsShell.test.tsx passed: 84 files, 1207 tests.
• pnpm --filter @markra/app build passed.

Risk

• Low: only resets scroll position on settings category changes.

Closes #313

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Project	Deployment	Actions	Updated (UTC)
markra-web	Ready	Preview, Comment	Jun 17, 2026 1:06pm