Problem

dash0 dashboards update -f <file> does not handle PersesDashboard CRD files correctly. It reads the file directly into a DashboardDefinition struct without detecting the kind first, so the PersesDashboard-specific conversion (v1alpha1/v1alpha2 normalization, dash0.com/id label extraction, annotation mapping) is skipped.

Same root cause as #110: apply and dashboards create detect the kind and route to the PersesDashboard parser, but dashboards update was missed when CRD support was added.

Expected behavior

dashboards update should accept PersesDashboard CRD files, matching the behavior of apply and dashboards create.