fix(security): reserve dashboard hosts from NAT and re-check DDNS profile ownership at worker time

GHSA-x6fg-52vr-hj4w: NAT is a commonHandler any authenticated member can
create, and newHTTPandGRPCMux matches r.Host against NAT before dispatching
the dashboard/gRPC handlers, so a member could register the dashboard's own
host as a NAT Domain and hijack global routing. Add IsReservedDashboardHost
(InstallHost/ListenHost plus an operator-declared ReservedHosts list for
reverse-proxy deployments), reject reserved hosts on create/update, and drop
pre-planted records when building the startup cache.

GHSA-39g2-8x68-pmx8: bind-time CheckPermission let a member pre-bind a DDNS
profile ID that the victim would only create later. GetDDNSProvidersFromProfiles
now re-validates ownership by server owner UID and skips foreign-owned
profiles (UserID==0 is treated as a migration artifact, not an admin grant).

Co-authored-by: cloudcode <cloudcode@users.noreply.github.com>

model/setting_api.go

@@ -8,6 +8,7 @@ type SettingForm struct {
 	SiteName                    string `json:"site_name,omitempty" minLength:"1"`
 	Language                    string `json:"language,omitempty" minLength:"2"`
 	InstallHost                 string `json:"install_host,omitempty" validate:"optional"`
+	ReservedHosts               string `json:"reserved_hosts,omitempty" validate:"optional"`
 	CustomCode                  string `json:"custom_code,omitempty" validate:"optional"`
 	CustomCodeDashboard         string `json:"custom_code_dashboard,omitempty" validate:"optional"`
 	WebRealIPHeader             string `json:"web_real_ip_header,omitempty" validate:"optional"`   // 前端真实IP