fix: permission checks for speedId and inPort + multi-node IP constraints (#261)

* feat: restrict user permissions and multi-node IP constraints

- Non-admin users cannot set speedId or inPort on forward create/update
- Multi-entrance tunnels disable custom listen IP for forwards
- Multi-exit tunnels disable custom connect IP
- Multi-node hop chains disable custom connect IP per hop
- Remove tunnel-first-IP fallback in forward ingress resolution
- Add contract tests for non-admin permission restrictions

Entire-Checkpoint: 133693290660

* fix: allow non-admin users to submit null speedId and zero inPort

- Backend: Check speedId is not nil before rejecting non-admin requests
- Backend: Only reject inPort if value > 0 for non-admin users
- Frontend: Only include speedId and inPort in payload for admin users
- Tests: Add contract tests for null speedId and zero inPort cases

.entire/metadata/ses_34c3da705ffeatkv1UcEyO5F8N/summary.txt

@@ -0,0 +1,6 @@
+Tag `2.1.7-beta4` 已在 GitHub 远程创建成功。
+
+**完成摘要：**
+- 提交: `7efb49b` - fix: handle forward service rebind on self-occupied port
+- PR: https://github.com/Sagit-chu/flvx/pull/257 (已合并)
+- Tag: `2.1.7-beta4` 已推送到远程