Add immediate regex validation to library filter and rename forms

[Copilot]

Users can enter invalid regex patterns in library filter and rename rules, causing runtime errors during application with non-obvious feedback. This adds client-side validation that shows errors immediately as users type.

Changes

Validation Logic

• Created RegexValidator helper class with IsValidRegex() method
• Validates patterns by attempting Regex.Match() and catching ArgumentException
• Applied to both EditLibraryFilterForm and EditLibraryRenameForm components

UI Feedback

• Added Error and ErrorText attributes to pattern input fields
• Validation only triggers when PatternType is Regex (not Contains)
• Error text appears immediately with Immediate="true" binding

Localization

• Added Error_InvalidRegex resource key in en-US, de-DE, ja-JP
• Fallback to English text if localization missing

Example

private bool IsPatternInvalid => 
    FilterRule.PatternType == LibraryFilterPatternType.Regex && 
    !string.IsNullOrWhiteSpace(FilterRule.Pattern) && 
    !RegexValidator.IsValidRegex(FilterRule.Pattern);

Screenshots

Invalid regex in filter rules:

Invalid regex in rename rules:

Original prompt

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This section details on the original issue you should resolve

<issue_title>Check regex in the filtering and name change features for validity before saving</issue_title>
<issue_description>This would protect against potentially invalid regex's being entered with the mistake being non-obvious. If possible, feedback should be immediate.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Check regex in the filtering and name change features for validity before saving #275

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