TP-28 — Performance test: 50+ themes in picker

[ZhuchkaTriplesix]

Epic: E
Depends on: TP-18, TP-21

Source: docs/theme-parser-github-issues.md

Goal

Prevent regression where many themes make Preferences slow or overflow.

Files

• test/features/settings/theme_picker_button_test.dart
• maybe test/features/settings/preferences_appearance_section_test.dart

Implementation

Create 60 fake ThemeDefinition objects.

Test:

• picker opens;
• only visible subset is built if measurable;
• no overflow exception;
• scroll to bottom works;
• select last item works.

If exact build count is hard to assert, assert behavior and no exceptions.

Acceptance Criteria

• Test fails if picker uses unbounded Column and overflows.
• Test passes with ListView.builder.

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