feat(card-browser): implement 'Default search text'

[david-allison]

Note

Assisted-by: Claude Opus 4.7

Purpose / Description

Upstream functionality, only implemented in the new card browser

Fixes

• Fixes Card Browser: Implement 'Default search text' #18618

Approach

I performed a few initial refactors, partially as logic shouldn't be in the saveChanges method, partially to reduce the code in the ViewModel

• Adds a 'Default search text' control to the Browser options
• If set, uses this as the default search text
  • Only if the search text wasn't set through other means (intent etc...)

How Has This Been Tested?

Unit tests

Checklist

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner
  • I have fixed all but a contrast warning(light mode only), which falsely detects that the border should meet the standard for text (3.0:1 is for for the border, it wants 4.5:1). This change would negatively impact the visual hierarchy: the border should be less prominent than the hint

[Giyutomioka-SS]

LGTM - has a merge conflict to resolve.