fix versionMatcher: use non-capturing group (?:-dirty)? for gorilla/mux

gorilla/mux explicitly rejects capturing groups () in route regexps,
only non-capturing groups (?:) are allowed. The original regex was
missing the ? to make -dirty optional.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pkg/apiserver/apiserver.go

@@ -40,7 +40,7 @@ import (
 
 // versionMatcher defines a variable matcher to be parsed by the router
 // when a request is about to be served.
-const versionMatcher = "/v{version:[0-9.]+(-dirty)?}"
+const versionMatcher = "/v{version:[0-9.]+(?:-dirty)?}"
 
 // Config provides the configuration for the API server
 type Config struct {