feat(icon): add ItIconRegistryService for custom SVG icons

[giulio-leone]

Closes #563

What

Adds ItIconRegistryService — a root-provided service that allows registering custom SVG icons by name, so they can be rendered using <it-icon name="my-custom"> alongside built-in Bootstrap Italia sprite icons.

How it works

Three registration methods:

1. Inline SVG — registerIcon(name, svgContent) / registerIcons(record)

   const registry = inject(ItIconRegistryService);
   registry.registerIcon('custom-home', '<path d="M10 20v-6h4v6..."/>');

2. External sprite — registerIconFromSprite(name, url, fragmentId)

   registry.registerIconFromSprite('custom-star', '/assets/sprites.svg', 'star');

3. Bulk — registerIcons(icons)

Resolution priority: Custom inline SVG → Custom sprite → Built-in BI sprite

Component changes:

• ItIconComponent now injects ItIconRegistryService and checks it before falling back to the built-in sprite
• Template uses @if (isCustomInlineSvg) to conditionally render <g [innerHTML]> for inline SVGs vs <use> for sprites
• name input type widened to IconName | string to accept custom names

API surface

@Injectable({ providedIn: 'root' })
export class ItIconRegistryService {
  registerIcon(name: string, svgContent: string): void;
  registerIcons(icons: Record<string, string>): void;
  registerIconFromSprite(name: string, spriteUrl: string, fragmentId: string): void;
  hasIcon(name: string): boolean;
  getIconSvg(name: string): SafeHtml | undefined;
  getIconSpriteHref(name: string): string | undefined;
  removeIcon(name: string): boolean;
  clear(): void;
}

Test coverage

27 new tests covering:

• Built-in sprite rendering (href, no <g>)
• CSS class propagation (size, color, padded, svgClass)
• Accessibility (aria-hidden, title, labelWaria)
• Custom inline SVG rendering (correct DOM, no <use>)
• Custom sprite rendering (custom href in <use>)
• Fallback to built-in sprite when no custom icon registered
• Name collision: custom takes precedence over built-in
• Bulk registration, removal, clear
• Registry unit operations (hasIcon, getIconSvg, getIconSpriteHref, removeIcon)

136/136 tests passing, 0 lint errors (only pre-existing warnings).

⚠️ This reopens #641 which was accidentally closed due to fork deletion.

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Project	Deployment	Actions	Updated (UTC)
design-angular-kit	Error		Mar 27, 2026 3:50pm