feat: trusted release keys setting; drop the duplicate release registration route [CI]

The panel now lets the deployer decide which release keys it trusts. The
official CI key is built in and always trusted; an own P-256 public key can be
added (off by default, the private key is rejected) so manifests signed with it
are accepted too. Removing it drops the manifests only it signed. Changes are
audited and need update.confirm.

Admin UI: System > Trust > "Trusted release keys" with a collapsible guide on
generating a key pair and signing a manifest with openssl.

Registration now has one path, POST /api/release/offer (no token, signature
verified). The admin POST /releases route, the release.publish capability and
the ci-release preset are removed.

backend/tests/MoShiro.Backend.Tests/UpdateTests.cs

@@ -26,8 +26,11 @@ public sealed class UpdateTests
     private static string Manifest(string component, long seq, string digest = Digest) =>
         $$"""{"schema":1,"component":"{{component}}","channel":"dev","image":"registry.example/moshiro-dev/moshiro-{{component}}","digest":"{{digest}}","tag":"dev-{{seq}}","version":"0.1.1","commit":"abc","built_at":"2026-10-06T00:00:00Z","seq":{{seq}}}""";
 
-    private async Task<HttpResponseMessage> PublishAsync(string manifest, string? signature = null) =>
-        await _backend.Admin.PostAsync("/api/admin/releases", BackendFixture.Json(new JsonObject { ["manifest"] = manifest, ["signature"] = signature ?? TestReleaseKey.Sign(manifest) }));
+    private async Task<HttpResponseMessage> PublishAsync(string manifest, string? signature = null)
+    {
+        signature ??= TestReleaseKey.Sign(manifest);
+        return await _backend.Anonymous.PostAsync("/api/release/offer", BackendFixture.Json(new JsonObject { ["manifest"] = manifest, ["signature"] = signature }));
+    }
 
     [Fact]
     public async Task Release_IsForwardedByteForByte_ToOnlineNodesOfThatComponent_AndToNodesThatConnectLater()
@@ -57,13 +60,13 @@ public sealed class UpdateTests
     }
 
     [Fact]
-    public async Task Release_Registration_RefusesBadManifests_StaleSeq_AndNeedsAnAdmin()
+    public async Task Release_Registration_RefusesBadManifests_BadSignatures_AndStaleSeq()
     {
         long seq = NextSeq();
         Assert.Equal(HttpStatusCode.BadRequest, (await PublishAsync("{not json")).StatusCode);
         Assert.Equal(HttpStatusCode.BadRequest, (await PublishAsync(Manifest("agent", seq, digest: "sha256:short"))).StatusCode);
         Assert.Equal(HttpStatusCode.BadRequest, (await PublishAsync(Manifest("unknown", seq))).StatusCode);
-        Assert.Equal(HttpStatusCode.BadRequest, (await PublishAsync(Manifest("agent", seq), signature: "not base64!")).StatusCode);
+        Assert.Equal(HttpStatusCode.Forbidden, (await PublishAsync(Manifest("agent", seq), signature: "not base64!")).StatusCode);
 
         using var other = System.Security.Cryptography.ECDsa.Create(System.Security.Cryptography.ECCurve.NamedCurves.nistP256);
         string foreign = Convert.ToBase64String(other.SignData(System.Text.Encoding.UTF8.GetBytes(Manifest("agent", seq)), System.Security.Cryptography.HashAlgorithmName.SHA256, System.Security.Cryptography.DSASignatureFormat.Rfc3279DerSequence));
@@ -73,43 +76,6 @@ public sealed class UpdateTests
         Assert.Equal(HttpStatusCode.Created, (await PublishAsync(Manifest("agent", seq))).StatusCode);
         Assert.Equal(HttpStatusCode.Conflict, (await PublishAsync(Manifest("agent", seq))).StatusCode); // 同一个 seq：重放
         Assert.Equal(HttpStatusCode.Conflict, (await PublishAsync(Manifest("agent", seq - 1))).StatusCode); // 更旧的 seq
-
-        using HttpResponseMessage anonymous = await _backend.Anonymous.PostAsync("/api/admin/releases", BackendFixture.Json(new JsonObject { ["manifest"] = Manifest("agent", seq + 1), ["signature"] = TestReleaseKey.Sign(Manifest("agent", seq + 1)) }));
-        Assert.Contains(anonymous.StatusCode, new[] { HttpStatusCode.Unauthorized, HttpStatusCode.Forbidden });
-    }
-
-    [Fact]
-    public async Task ReleaseToken_CanOnlyRegisterReleases_AndAReadTokenCannotEvenDoThat()
-    {
-        async Task<string> NewTokenAsync(params string[] capabilities)
-        {
-            using HttpResponseMessage created = await _backend.Admin.PostAsync("/api/admin/api-tokens", BackendFixture.Json(new JsonObject { ["name"] = _backend.UniqueName("ci"), ["capabilities"] = BackendFixture.Capabilities(capabilities) }));
-            Assert.Equal(HttpStatusCode.Created, created.StatusCode);
-            return JsonNode.Parse(await created.Content.ReadAsStringAsync())!["plaintext"]!.GetValue<string>();
-        }
-
-        HttpClient Client(string token)
-        {
-            var client = new HttpClient { BaseAddress = _backend.BaseAddress };
-            client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", token);
-            return client;
-        }
-
-        long seq = NextSeq();
-        using HttpClient release = Client(await NewTokenAsync("release.publish"));
-        using HttpClient read = Client(await NewTokenAsync("public.read", "fleet.read"));
-        var body = BackendFixture.Json(new JsonObject { ["manifest"] = Manifest("probe", seq), ["signature"] = TestReleaseKey.Sign(Manifest("probe", seq)) });
-
-        using HttpResponseMessage forbidden = await read.PostAsync("/api/admin/releases", BackendFixture.Json(new JsonObject { ["manifest"] = Manifest("probe", seq), ["signature"] = TestReleaseKey.Sign(Manifest("probe", seq)) }));
-        Assert.Equal(HttpStatusCode.Forbidden, forbidden.StatusCode);
-        using HttpResponseMessage published = await release.PostAsync("/api/admin/releases", body);
-        Assert.Equal(HttpStatusCode.Created, published.StatusCode);
-
-        // release 令牌只能登记发布清单：读不了任何东西，也不能做别的管理操作
-        Assert.Equal(HttpStatusCode.Forbidden, (await release.GetAsync("/api/admin/agents")).StatusCode);
-        Assert.Equal(HttpStatusCode.Forbidden, (await release.GetAsync("/api/admin/releases")).StatusCode);
-        Assert.Equal(HttpStatusCode.Forbidden, (await release.PostAsync("/api/admin/nodes/agt_x/update", null)).StatusCode);
-        Assert.Equal(HttpStatusCode.Unauthorized, (await _backend.Anonymous.PostAsync("/api/admin/releases", BackendFixture.Json(new JsonObject { ["manifest"] = Manifest("probe", seq + 1), ["signature"] = TestReleaseKey.Sign(Manifest("probe", seq + 1)) }))).StatusCode);
     }
 
     [Fact]