Align DEFAULT_HISTORY_PAGE_SIZE with the standalone server (200 -> 500)

Closes #298. The workflow package's WorkerProtocolVersion constant and
the standalone server's history_page_size_default config had drifted:
the package constant read 200 while the server advertises 500 in its
server_capabilities response. The server is the authority on pagination
size, so external workers already receive 500 at runtime; the constant
was creating a documentation mismatch for SDK authors who referenced it.

The package constant is the contract default that external workers and
SDK authors should assume when the server has not advertised a value.
Updated the docblock to name the authoritative server config key so
future drift is obvious.

14 WorkerProtocolVersion tests (49 assertions) still pass — they
reference the constant symbolically, not the literal value.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: durable-workflow-ops

src/V2/Support/WorkerProtocolVersion.php

@@ -31,8 +31,14 @@ final class WorkerProtocolVersion
 
     /**
      * Default page size for paginated history responses.
+     *
+     * Aligned with the standalone server's WORKFLOW_SERVER_HISTORY_PAGE_SIZE_DEFAULT
+     * default (server.worker_protocol.history_page_size_default in config/server.php).
+     * The server is the authority on pagination size — this constant is the
+     * contract default that external workers and SDK authors should assume
+     * when the server has not advertised a value via server_capabilities.
      */
-    public const DEFAULT_HISTORY_PAGE_SIZE = 200;
+    public const DEFAULT_HISTORY_PAGE_SIZE = 500;
 
     /**
      * Maximum allowed page size for paginated history responses.