fix: support lowercase proxy environment variables as fallback

[EvanYao826]

Summary

The plugin_daemon config only reads uppercase HTTP_PROXY, HTTPS_PROXY, and NO_PROXY via envconfig tags. When only lowercase http_proxy, https_proxy, and no_proxy are set (common in many environments), the proxy settings are silently ignored, causing plugin installation failures behind HTTP proxies.

Add fallback in SetDefault() to check lowercase env vars when uppercase are not set, matching the behavior of other Dify containers (api, web).

Fix

In internal/types/app/default.go, use the existing setDefaultString helper function for proxy environment variable fallback to maintain code consistency.

Checklist

• I have read the Contributing Guide
• Fixes #18752

[gemini-code-assist]

Code Review

This pull request updates the SetDefault function in internal/types/app/default.go to include fallbacks for proxy environment variables (http_proxy, https_proxy, and no_proxy) when their uppercase counterparts are not set. The review feedback suggests utilizing the existing setDefaultString helper function to implement these fallbacks more concisely and maintain consistency with the rest of the function.

[gemini-code-assist]

For better maintainability and consistency with the rest of the SetDefault function, use the existing setDefaultString helper. This reduces boilerplate while maintaining the same logic.

Suggested change

	if config.HttpProxy == "" {
	config.HttpProxy = os.Getenv("http_proxy")
	}
	if config.HttpsProxy == "" {
	config.HttpsProxy = os.Getenv("https_proxy")
	}
	if config.NoProxy == "" {
	config.NoProxy = os.Getenv("no_proxy")
	}
	setDefaultString(&config.HttpProxy, os.Getenv("http_proxy"))
	setDefaultString(&config.HttpsProxy, os.Getenv("https_proxy"))
	setDefaultString(&config.NoProxy, os.Getenv("no_proxy"))

[EvanYao826]

Thank you for the review! I will update the PR to use the existing setDefaultString helper function for consistency.