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_34da82e9effeFXu4pJM3CaFEQB/prompt.txt

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+提交全部变更并且push，创建pr合并，发布新tag，alpha版本

.entire/metadata/ses_34da82e9effeFXu4pJM3CaFEQB/summary.txt

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+✅ 完成：
+- **提交**: `fix: use configured connectIp for tunnel chain diagnosis` (1c10347)
+- **PR**: #248 已合并 → https://github.com/Sagit-chu/flvx/pull/248
+- **Tag**: `2.1.7-alpha8` 已创建并推送
+
+变更内容：修复了隧道链诊断时使用配置的 connectIp、forward 绑定 IP 支持带端口的地址、添加了全面的测试覆盖。