feat: integrate client and server sharing workflows

server/src/WebDrop.Api/ApiContract.cs

@@ -0,0 +1,7 @@
+namespace WebDrop.Api;
+
+public static class ApiContract
+{
+    // Keep this aligned with contracts/api-contract.json and docs/openapi.yaml.
+    public const string Version = "1.0.0";
+}

server/src/WebDrop.Api/ApiJson.cs

@@ -17,6 +17,7 @@ public sealed class GoneLogBody
 public sealed class ServerInfoBody
 {
     [JsonPropertyName("protocol")] public int Protocol { get; init; } = 1;
+    [JsonPropertyName("contract_version")] public string ContractVersion { get; init; } = ApiContract.Version;
     [JsonPropertyName("captcha")] public required CaptchaBody Captcha { get; init; }
     [JsonPropertyName("transports")] public required TransportsBody Transports { get; init; }
     [JsonPropertyName("limits")] public required LimitsBody Limits { get; init; }