When two or more nodes have an identical matcher rule they receive
identical default priority (rule string length). The priority shortcut
assumed the top-priority node was the single authoritative choice and
returned it directly, bypassing the selector (FailFilter, BackupFilter,
strategy) — so weight, round-robin, and hash were silently ignored.
Add a third condition: the top priority must be strictly greater than
the second-highest. When multiple nodes share the same highest priority
the selector applies normally for load balancing.
Add doc comments on NodeMatcherConfig.Priority explaining the three
semantic ranges (0=auto, negative=always-selector, positive=shortcut).