refactor(config): centralize env loading and enforce typed access

- Centralize environment variable loading in config.MustLoad
- Parse and validate all env vars once at initialization
- Make config fields private and read-only
- Remove public Getenv usage in favor of typed accessors
- Improve validation and initialization order
- Normalize enum naming to be idiomatic and avoid constant collisions

session/interaction/slug.go

@@ -15,7 +15,7 @@ import (
 func (m *model) slugUpdate(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 	var cmd tea.Cmd
 
-	if m.tunnelType != types.HTTP {
+	if m.tunnelType != types.TunnelTypeHTTP {
 		m.editingSlug = false
 		m.slugError = ""
 		return m, tea.Batch(tea.ClearScreen, textinput.Blink)
@@ -30,10 +30,10 @@ func (m *model) slugUpdate(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 		inputValue := m.slugInput.Value()
 		if err := m.interaction.sessionRegistry.Update(m.interaction.user, types.SessionKey{
 			Id:   m.interaction.slug.String(),
-			Type: types.HTTP,
+			Type: types.TunnelTypeHTTP,
 		}, types.SessionKey{
 			Id:   inputValue,
-			Type: types.HTTP,
+			Type: types.TunnelTypeHTTP,
 		}); err != nil {
 			m.slugError = err.Error()
 			return m, nil
@@ -130,7 +130,7 @@ func (m *model) slugView() string {
 	b.WriteString(titleStyle.Render(title))
 	b.WriteString("\n\n")
 
-	if m.tunnelType != types.HTTP {
+	if m.tunnelType != types.TunnelTypeHTTP {
 		warningBoxWidth := getResponsiveWidth(m.width, 10, 30, 60)
 		warningBoxStyle := lipgloss.NewStyle().
 			Foreground(lipgloss.Color("#FFA500")).
@@ -145,9 +145,9 @@ func (m *model) slugView() string {
 
 		var warningText string
 		if isVeryCompact {
-			warningText = "⚠️ TCP tunnels don't support custom subdomains."
+			warningText = "⚠️ TunnelTypeTCP tunnels don't support custom subdomains."
 		} else {
-			warningText = "⚠️ TCP tunnels cannot have custom subdomains. Only HTTP/HTTPS tunnels support subdomain customization."
+			warningText = "⚠️ TunnelTypeTCP tunnels cannot have custom subdomains. Only TunnelTypeHTTP/HTTPS tunnels support subdomain customization."
 		}
 		b.WriteString(warningBoxStyle.Render(warningText))
 		b.WriteString("\n\n")