README: describe unregister_resource accurately (not a deprecated alias)

unregister_resource is NOT [[deprecated]] and NOT an alias for
unregister_path — it atomically clears either an exact or a prefix
registration (a capability unregister_path alone lacks). Correct the
stale wording; the method stays.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NpysYDDJac63yz2mZKKiDf

Author: etr

README.md

@@ -879,8 +879,10 @@ Regex validation is on by default; disable with `regex_checking(false)`
 on the builder if you need pure literal-path semantics.
 
 **Unregistration.** `unregister_path(path)` and `unregister_prefix(path)`
-remove a previously registered resource by path. (`unregister_resource`
-exists as a deprecated alias for `unregister_path`.)
+remove an exact-match or prefix-match registration respectively.
+`unregister_resource(path)` is a kind-agnostic convenience that atomically
+clears whichever kind (exact or prefix) is registered at `path` — use it
+when the caller does not track how the resource was registered.
 
 ## Request