fix(filters): make sure filters are replaced case-insensitively before filtering on the server

Resolves https://community.vikunja.io/t/filtering-startdate-now-is-invalid/2613

frontend/src/helpers/filters.test.ts

@@ -137,6 +137,16 @@ describe('Filter Transformation', () => {
 
 			expect(transformed).toBe('labels in 2 || labels in l')
 		})
+		
+		it('should correctly transform the cases of fields', () => {
+			const transformed = transformFilterStringForApi(
+				'startdate > now',
+				nullTitleToIdResolver,
+				nullTitleToIdResolver,
+			)
+
+			expect(transformed).toBe('start_date > now')
+		})
 	})
 
 	describe('To API', () => {

frontend/src/helpers/filters.ts

@@ -67,10 +67,16 @@ export function transformFilterStringForApi(
 	projectResolver: (title: string) => number | null,
 ): string {
 	
-	if (filter.trim() === '') {
+	filter = filter.trim()
+
+	if (filter === '') {
 		return ''
 	}
 	
+	AVAILABLE_FILTER_FIELDS.forEach(f => {
+		filter = filter.replace(new RegExp(f, 'ig'), f)
+	})
+
 	// Transform labels to ids
 	LABEL_FIELDS.forEach(field => {
 		const pattern = getFilterFieldRegexPattern(field)