Fix env var expansion skipping maps inside arrays

[Copilot]

• Fix expandConfigStrings to recurse into map[string]any items inside []any slices
• Add test for maps-inside-arrays env var expansion (multiple clients, deeply nested scopes)

---

🔒 GitHub Advanced Security automatically protects Copilot coding agent pull requests. You can protect all pull requests by enabling Advanced Security for your repositories. Learn more about Advanced Security.

[Copilot]

Pull request overview

This pull request fixes a bug in the expandConfigStrings function where environment variable placeholders like ${VAR} were not being expanded in map[string]any elements inside []any slices. This affected real-world configurations such as OAuth client arrays where credentials are stored as environment variables.

Changes:

• Added recursive expansion support for maps inside arrays by adding an else if branch in the array iteration logic
• Added comprehensive test coverage with TestExpandConfigStrings_ArrayOfMaps to verify the fix works correctly

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
engine.go	Added else if branch (lines 1000-1001) to recursively expand strings in maps found inside arrays, matching the existing pattern for top-level nested maps
engine_secrets_test.go	Added TestExpandConfigStrings_ArrayOfMaps test case (lines 118-142) to verify env var expansion works correctly for maps inside arrays, using OAuth client configuration as a realistic example

[intel352]

@copilot apply changes based on the comments in this thread