chore: export UserConfigSchema for consumers

[nirinchev]

Proposed changes

This will make it easier for library consumers (i.e. vscode) to construct a valid user config with all defaults.

[Copilot]

Pull request overview

This PR exports the UserConfigSchema from the library's public API to enable external consumers (such as the VSCode extension) to programmatically construct valid user configurations with proper defaults and validation.

Key Changes:

• Export UserConfigSchema alongside the existing UserConfig type from the library's entry point

[coveralls]

Pull Request Test Coverage Report for Build 19827900409

Details

• 3 of 4 (75.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.004%) to 80.468%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/lib.ts	0	1	0.0%

Totals
Change from base Build 19766295633:	-0.004%
Covered Lines:	6669
Relevant Lines:	8205

---

💛 - Coveralls

[himanshusinghs]

Just to mention - #767 covers this so if its not urgent shall we wait for that to land. Happy to have this merged as well.