fix(tui): skip irrelevant field validation by monitor type

URL, SSL threshold, and port validators blocked form progression
when editing monitors that don't use those fields (e.g. ping monitors
failing URL validation, non-SSL sites failing threshold check).

Scope each validator to fire only for its relevant monitor type.

internal/tui/tab_sites.go

@@ -509,7 +509,7 @@ func (m *Model) initSiteHuhForm() tea.Cmd {
 				Description("Required for HTTP monitors").
 				Value(&m.siteFormData.URL).
 				Validate(func(s string) error {
-					if m.siteFormData.SiteType == "push" || m.siteFormData.SiteType == "group" {
+					if m.siteFormData.SiteType != "http" {
 						return nil
 					}
 					if s == "" {
@@ -555,12 +555,15 @@ func (m *Model) initSiteHuhForm() tea.Cmd {
 				Description("Target port for TCP port monitors").
 				Value(&m.siteFormData.Port).
 				Validate(func(s string) error {
+					if m.siteFormData.SiteType != "port" {
+						return nil
+					}
 					v, err := strconv.Atoi(s)
 					if err != nil {
 						return fmt.Errorf("must be a number")
 					}
-					if v < 0 || v > 65535 {
-						return fmt.Errorf("port must be 0-65535")
+					if v < 1 || v > 65535 {
+						return fmt.Errorf("port must be 1-65535")
 					}
 					return nil
 				}),
@@ -615,6 +618,9 @@ func (m *Model) initSiteHuhForm() tea.Cmd {
 				Placeholder("7").
 				Value(&m.siteFormData.Threshold).
 				Validate(func(s string) error {
+					if !m.siteFormData.CheckSSL {
+						return nil
+					}
 					v, err := strconv.Atoi(s)
 					if err != nil {
 						return fmt.Errorf("must be a number")