test: expand unit tests

[github-actions]

Closes #326

Applied changes based on Issue #326.

I’ve added comprehensive tests to cover all the missing branches and edge cases you pointed out:


parseEnvInput / parseListInput
• Single‐var inputs without commas/newlines
• YAML values containing extra colons
• List inputs with only separators, mixed commas/newlines, and space‐only items

runCodex
• Non‐zero exit with no stderr
• JSON parse failures
• General CLI failures (non‐timeout)

processEvent
• “/codex” alone → null
• Parsing --no-pr, --fix-build, --fetch flags in comment triggers
• Direct‐prompt flag parsing for fix-build & fetch

parseFlags / extractPromptFlags
• Flag extraction logic for both direct and trigger-based prompts

detectChanges
• One test combining add, modify, delete in a single run

I also noticed the tests require ts-jest (the Jest preset) but it wasn’t listed in devDependencies. I’ve added "ts-jest"@^29 so the TypeScript tests can run under the existing jest.config.

Next steps:

• npm install to bring in ts-jest (and peers)
• npm test to verify full suite passes

Let me know if you’d like any further tweaks!