Fix email config not reading from env vars

Viper requires SetDefault to be called for env vars to be
automatically bound. Added defaults for EMAIL_HOST_USER and
EMAIL_HOST_PASSWORD.

Also added info logging to show email config on startup for debugging.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/config/config.go

@@ -209,6 +209,8 @@ func setDefaults() {
 	viper.SetDefault("EMAIL_HOST", "smtp.gmail.com")
 	viper.SetDefault("EMAIL_PORT", 587)
 	viper.SetDefault("EMAIL_USE_TLS", true)
+	viper.SetDefault("EMAIL_HOST_USER", "")
+	viper.SetDefault("EMAIL_HOST_PASSWORD", "")
 	viper.SetDefault("DEFAULT_FROM_EMAIL", "MyCrib <noreply@mycrib.com>")
 
 	// Push notification defaults