Arc Enterprise cluster FSM applyRegisterFile accepts arbitrary file paths without validation, enabling cluster-wide path-traversal worm primitive

Arc is an open, SQL-native time-series database for telemetry. Prior to version 26.06.1, Arc Enterprise's Raft FSM (`internal/cluster/raft/fsm.go:applyRegisterFile`) accepts attacker-chosen file paths in manifest-registration proposals without validating them against the configured storage backend. The only check is that the path is non-empty. There is no parent-traversal (`..`) rejection, no allowlist of legitimate prefixes, no scheme restriction (`s3://` vs local), and no length bound. This is fixed in 2026.06.1. Some workarounds are available. Restrict cluster network access to known-trusted peers via strict firewall rules, audit the cluster manifest for unexpected paths (any path not matching the configured storage backend root is suspect), and/or disable cluster mode until the fix is available.