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.

docs/enrollment.md

@@ -10,7 +10,7 @@
 | Probe | Fleet 节点身份（连面板）+ 另一把独立的密钥（连 Agent，放在 `tls.pfx`） | `fleet-enroll`，和 Agent 一样用加入令牌（`role=probe`）；可以有多个 Probe，每个独立吊销 | 两把公钥 |
 | 面板用户 | 账号 + 密码（PBKDF2-SHA256） | 面板 | 密码哈希 |
 | API 令牌 | 随机高熵令牌，带一组能力（见 [access.md](access.md)） | 面板 | SHA-256 |
-| 发布签名 | ECDSA P-256 发布密钥 | CI（Woodpecker 密钥 `release_signing_key`）或离线环境 | 只在节点宿主机的更新器里配置公钥（容器节点是 `moshiro-update`，见 [deployment.md](deployment.md)；纯二进制节点的更新是待办），**面板不保存私钥，也不验签** |
+| 发布签名 | ECDSA P-256 发布密钥 | CI（Woodpecker 密钥 `release_signing_key`）或离线环境 | 只在节点宿主机的更新器里配置公钥（容器节点是 `moshiro-update`，见 [deployment.md](deployment.md)；纯二进制节点的更新是待办），**面板不保存私钥**；登记清单时面板用公钥验签，节点宿主机的更新器之后再验一次 |
 
 ## 2. Agent 接入流程