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/Server/Builder.php

@@ -473,11 +473,12 @@ final class Builder
     public function addPrompt(
         \Closure|array|string $handler,
         ?string $name = null,
+        ?string $title = null,
         ?string $description = null,
         ?array $icons = null,
         ?array $meta = null,
     ): self {
-        $this->prompts[] = compact('handler', 'name', 'description', 'icons', 'meta');
+        $this->prompts[] = compact('handler', 'name', 'title', 'description', 'icons', 'meta');
 
         return $this;
     }