fix: restrict file permissions and document CLI path usage (CWE-276,22)

[Vaishnav88sk]

Description

This PR addresses several file-related security warnings identified by the gosec SAST scanner.
Security Fixes (CWE-276):

• G301 / G302: Configuration directories and files were being created with overly permissive access (os.ModePerm / 0644). This has been restricted to 0750 for directories and 0600 for files so that only the owner has access.

False Positive Suppressions (CWE-22):

• G304 / G703: The scanner flagged potential path traversal risks on os.ReadFile and os.Open. Because this is a local CLI tool, the user intentionally provides these paths (e.g., via CLI flags) or they are sourced from trusted system variables (e.g., GITHUB_OUTPUT). These have been annotated with #nosec to suppress the warnings and document the design choice.

How to test

1. Run gosec -include=G301,G302,G304,G703 ./... and verify 0 issues are found.
2. Run the CLI to generate a local config and verify the directory is created with rwxr-x--- (0750) permissions.

[Harsh4902]

LGTM

[github-actions]

🎉 @Vaishnav88sk

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