refactor: remove the runtime binary binding; every release registration path verifies the CI signature [CI]

The hash a node reports about itself cannot be trusted (a swapped binary can
copy the old hash), so the runtime binding only caught files that were replaced
by something that did not lie. Provenance stays where it can be verified: the
signed release manifest (digest) and the signed SHA256SUMS.

- Remove BinaryBindingService, the node_bindings table (schema v15 drops it),
  BinaryPolicy, the handshake hash/manifest fields and the admin binary column.
- Drop the per-platform "binaries" list from the release manifest, the hash
  scripts and the updater's installed.manifest copy.
- ReleaseService.PublishAsync now verifies the release signature, so the admin
  POST /releases route is no longer an unsigned path; tests sign with a test key.
- Docs: section 16 explains why the runtime check is gone.

backend/fleet/src/Fleet.Link/FleetLink.cs

@@ -72,9 +72,6 @@ public sealed class FleetLinkOptions
     /// 服务器必须在挑战里证明自己，之后这条链路用应用层加密；否则按旧的方式（没有固定信任根的节点）。
     /// </summary>
     public IServerVerifier? ServerVerifier { get; init; }
-
-    /// <summary>握手时自述正在运行的二进制（哈希和 CI 签名的清单）；没有就不上报（旧行为）。</summary>
-    public Func<BinaryAttestation?>? Attestation { get; init; }
 }
 
 /// <summary>
@@ -226,16 +223,6 @@ public sealed class FleetLink
     }
 
     /// <summary>挑战 → 签名 → 认证结果。失败返回原因；服务端禁用该节点时不再重试。</summary>
-    private void Attest(AuthParams auth)
-    {
-        if (_options.Attestation?.Invoke() is { } attestation)
-        {
-            auth.Binary = attestation.Sha256;
-            auth.Release = attestation.Manifest;
-            auth.ReleaseSignature = attestation.Signature;
-        }
-    }
-
     private async Task<string?> AuthenticateAsync(SecureTransport transport, CancellationToken ct)
     {
         using var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(15), _time);
@@ -270,7 +257,6 @@ public sealed class FleetLink
                     Signature = Convert.ToBase64String(_options.Identity.Sign(SignaturePurpose.AuthSecure, _options.NodeId.Value, nonce.Nonce, serverEphemeralText, nodeEphemeralText)),
                     NodeEphemeral = nodeEphemeralText,
                 };
-                Attest(authParams);
                 RpcMessage secureRequest = RpcMessage.Request(1, FleetMethods.Auth, authParams, FleetRpcContext.Default.AuthParams);
                 await transport.SendAsync(new RpcFrame(FrameKind.Text, JsonSerializer.SerializeToUtf8Bytes(secureRequest, FleetRpcContext.Default.RpcMessage)), linked.Token);
                 transport.Enable(LinkCipher.ForNode(ephemeral, serverEphemeral, nonce.Nonce));
@@ -278,7 +264,6 @@ public sealed class FleetLink
             else
             {
                 authParams = new AuthParams { NodeId = _options.NodeId.Value, Signature = Convert.ToBase64String(_options.Identity.Sign(SignaturePurpose.Auth, _options.NodeId.Value, nonce.Nonce)) };
-                Attest(authParams);
                 RpcMessage request = RpcMessage.Request(1, FleetMethods.Auth, authParams, FleetRpcContext.Default.AuthParams);
                 await transport.SendAsync(new RpcFrame(FrameKind.Text, JsonSerializer.SerializeToUtf8Bytes(request, FleetRpcContext.Default.RpcMessage)), linked.Token);
             }