UX improvements: standardized labels, inline validation on field forms, settings page enhancements

UX improvements to make field validation more intuitive for non-technical users.

Changes

1. Inline validation on field configuration forms

• Validation rules now appear directly on field edit forms
• Positioned after "Required field" setting to group validation options together

2. Human-readable constraint labels

• Clear titles for all constraints (e.g., "At Least (>=)" instead of
  "GreaterThanOrEqual")
• Standardized form labels (e.g., "Minimum length", "Too short error")
• Helpful descriptions for non-technical users

3. Improved settings page

• Configure which constraints are available site-wide
• Category descriptions explaining each validation type

4. Token support

Added "Supports tokens" notes to comparison constraints. Changed numeric fields to textfield to
allow token input.

5. New LineCount constraint

Validates minimum/maximum number of lines in text fields.

Testing

• Module installs without errors on Drupal 11.2
• Validation works via entity save (compatible with JSON:API)