feat: added custom config support

[Gustash]

Closes #13

[Copilot]

Pull request overview

This PR adds support for custom configuration directory paths through a new --config-path command-line flag. This allows users to specify an alternative location for the application's configuration files instead of using the default directory.

Key Changes:

• Added --config-path flag to allow users to specify a custom configuration directory
• Renamed testConfigDir to overrideConfigDir to better reflect its dual purpose (testing and custom config)
• Updated all test files to use the renamed variable

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
main.go	Added configPath flag, import for auth package, and logic to set custom config directory using absolute paths
go.mod	Moved github.com/google/shlex from indirect to direct dependency
auth/config.go	Renamed testConfigDir to overrideConfigDir and added OverrideConfigDir function for public use
auth/session_test.go	Updated variable references from testConfigDir to overrideConfigDir
auth/userinfo_test.go	Updated variable references from testConfigDir to overrideConfigDir

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.