feat(fonts): implement Phase 3 - Update Filter Mapper

- Changed return type to Partial<ProxyFontsParams>
- Map providers array to single provider value (or undefined)
- Map categories array to single category value (or undefined)
- Map subsets array to single subset value (or undefined)
- Added type assertions for proper TypeScript compatibility

Phase 3/7: Proxy API Integration for GlyphDiff

src/features/GetFonts/lib/mapper/mapManagerToParams.ts

@@ -1,18 +1,56 @@
-import type { FontshareParams } from '$entities/Font';
+import type { ProxyFontsParams } from '$entities/Font/api';
 import type { FilterManager } from '../filterManager/filterManager.svelte';
 
 /**
- * Maps filter manager to fontshare params.
+ * Maps filter manager to proxy API parameters.
  *
- * @param manager - Filter manager instance.
- * @returns - Partial fontshare params.
+ * Transforms UI filter state into proxy API query parameters.
+ * Handles conversion from filter groups to API-specific parameters.
+ *
+ * @param manager - Filter manager instance with reactive state
+ * @returns - Partial proxy API parameters ready for API call
+ *
+ * @example
+ * ```ts
+ * // Example filter manager state:
+ * // {
+ * //   queryValue: 'roboto',
+ * //   providers: ['google'],
+ * //   categories: ['sans-serif'],
+ * //   subsets: ['latin']
+ * // }
+ *
+ * const params = mapManagerToParams(manager);
+ * // Returns: { provider: 'google', category: 'sans-serif', subset: 'latin', q: 'roboto' }
+ * ```
  */
-export function mapManagerToParams(manager: FilterManager): Partial<FontshareParams> {
+export function mapManagerToParams(manager: FilterManager): Partial<ProxyFontsParams> {
+    const providers = manager.getGroup('providers')?.instance.selectedProperties.map(p => p.value);
+    const categories = manager.getGroup('categories')?.instance.selectedProperties.map(p =>
+        p.value
+    );
+    const subsets = manager.getGroup('subsets')?.instance.selectedProperties.map(p => p.value);
+
     return {
-        q: manager.debouncedQueryValue,
-        // Map groups to specific API keys
-        categories: manager.getGroup('categories')?.instance.selectedProperties.map(p => p.value)
-            ?? [],
-        tags: manager.getGroup('tags')?.instance.selectedProperties.map(p => p.value) ?? [],
+        // Search query (debounced)
+        q: manager.debouncedQueryValue || undefined,
+
+        // Provider filter (single value - proxy API doesn't support array)
+        // Use first provider if multiple selected, or undefined if none/all selected
+        provider: providers && providers.length === 1
+            ? (providers[0] as 'google' | 'fontshare')
+            : undefined,
+
+        // Category filter (single value - proxy API doesn't support array)
+        // Use first category if multiple selected, or undefined if none/all selected
+        category: categories && categories.length === 1
+            ? (categories[0] as ProxyFontsParams['category'])
+            : undefined,
+
+        // Subset filter (single value - proxy API doesn't support array)
+        // Use first subset if multiple selected, or undefined if none/all selected
+        subset: subsets && subsets.length === 1
+            ? (subsets[0] as ProxyFontsParams['subset'])
+            : undefined,
     };
 }