Add search input to filter ReportBuilder column selection

[SimonBarrettACT]

Summary

• Add Alpine.js client-side search input to the report editor column selection panel, filtering columns and sections as the user types
• Add $enableColumnSearch property to WithReportBuilder trait (defaults to true, set to false to disable)
• Add 5 tests verifying the trait property, search markup, conditional rendering, and x-show filtering directives

Closes #111

Test plan

• Verify search input appears in the report editor panel
• Type a column name and confirm non-matching columns hide, matching columns remain visible
• Confirm entire sections hide when no columns in that section match
• Clear the search and verify all columns reappear
• Set $enableColumnSearch = false on a ReportBuilder subclass and verify the search input is absent
• Run composer test — all 7 tests pass

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