feat: add force refresh button to source/collection cards

- Backend: preview handlers accept forceRefresh in request body
- Frontend: Sources & Collections cards get a refresh button that
  bypasses cache and re-fetches from remote

internal/handler/crud.go

@@ -620,6 +620,13 @@ func getMapValue(v any) map[string]any {
 	return map[string]any{}
 }
 
+func getBoolValue(v any) bool {
+	if b, ok := v.(bool); ok {
+		return b
+	}
+	return false
+}
+
 func getStringArray(v any) []string {
 	if arr, ok := v.([]any); ok {
 		result := make([]string, 0, len(arr))

internal/handler/download_tools.go

@@ -183,6 +183,7 @@ func (d *Deps) HandlePreviewSource(c fiber.Ctx) error {
 		Target:           "json",
 		Settings:         settings,
 		RequestUserAgent: c.Get("User-Agent"),
+		ForceRefresh:     getBoolValue(input["forceRefresh"]),
 		CacheRepo:        d.CacheRepo,
 		ProxyURL:         d.Cfg.Fetcher.ProxyURL,
 	})
@@ -212,6 +213,7 @@ func (d *Deps) HandlePreviewCollection(c fiber.Ctx) error {
 		TemplateConfig:   d.getTemplateConfig(rec.TemplateId),
 		Settings:         settings,
 		RequestUserAgent: c.Get("User-Agent"),
+		ForceRefresh:     getBoolValue(input["forceRefresh"]),
 		CacheRepo:        d.CacheRepo,
 		ProxyURL:         d.Cfg.Fetcher.ProxyURL,
 	})