Currently the list of MCP protocol versions the package speaks is hardcoded inside Server.php:

protected array $supportedProtocolVersion = [
    '2025-11-25',
    '2025-06-18',
    '2025-03-26',
    '2024-11-05',
];

The upcoming MCP client (per the shipping plan) needs the same information — both sides need to agree on what versions exist, and the client needs to know which one is "latest" to send during the initialize handshake. Duplicating the list in two places will inevitably drift.

This PR moves the list into a shared enum, so server and client read from one place:

use Laravel\Mcp\Enums\ProtocolVersion;

ProtocolVersion::LATEST;        // V2025_11_25 (for the future client)
ProtocolVersion::supported();   // ['2025-11-25', '2025-06-18', '2025-03-26', '2024-11-05']

Servers that don't override the property continue to advertise the full supported list — no behavior change. If you want to pin a server to a single version, the override path stays the same as today:

class MyServer extends Server
{
    protected array $supportedProtocolVersion = [
        ProtocolVersion::V2025_11_25->value,
    ];
}