Add title field to Prompt for MCP spec compliance (#278)

The MCP 2025-11-25 specification defines an optional `title` property on
Prompt for human-readable display in UI contexts, distinct from the
programmatic `name` identifier. This was missing from the SDK.

BC Break: Builder::addPrompt() signature changed — $title parameter added
between $name and $description. Callers using positional arguments for
$description must switch to named arguments.

Closes #276

src/Capability/Registry/Loader/ArrayLoader.php

@@ -252,6 +252,7 @@ final class ArrayLoader implements LoaderInterface
                 }
                 $prompt = new Prompt(
                     name: $name,
+                    title: $data['title'] ?? null,
                     description: $description,
                     arguments: $arguments,
                     icons: $data['icons'] ?? null,