Function reportDiagnostic

The single emit path for the library's unsolicited diagnostics: the hook-failure fallback and the stateOwner keying warning. Both produce a structured AniLinkDiagnostic record so platform log collectors get filterable source/kind/hookName/requestId fields instead of prose.

Emission follows the configured DiagnosticsMode: "silent" suppresses the unsolicited output entirely; "hook" routes through onHookError only and never touches the console; "warn" routes through onHookError when configured, falling back to a console.warn of the JSON-serialized record. One exception: a diagnostic carrying a rawError (a real hook failure) always reaches a configured observer, in every mode. The modes control only the fallback. Exceptions from an observer are caught so a broken logger cannot break the request pipeline.