Add comprehensive test suite (71 tests)

[dines-rl]

Summary

• Farm.test.ts: Expanded with edge cases — empty arrays, multiple same-animal inputs, unrecognized animal types
• AstforFile.test.ts (new): 10 tests for `ASTForFile` and `ASTForFileToFile`, using mocked `tree-sitter` and `fs` modules to avoid native binary dependency
• GetDiffForFile.test.ts (new): 13 tests for `getSuggestionsFromGPT` with mocked OpenAI — covers successful suggestions, line number resolution (`determineLineStart`), null/error responses, and default parameter values
• IssuesTester.test.ts (new): 15 tests for the Probot `issues.opened` and `issues.closed` handlers, using a mock Probot app + mocked Runloop client
• index.test.ts (new): 16 tests for the `pull_request.opened/closed/reopened` handlers, covering devbox lifecycle, GPT integration, review comments, build failures, and error paths

Total: 71 tests across 5 test files — all passing.

Test plan

• `npm test` (vitest run) passes all 71 tests locally
• No real API calls made — OpenAI, Runloop, and tree-sitter are all mocked
• Edge cases covered: API failures, devbox not reaching running state, GPT returning no changes, build failures after applying changes

🤖 Generated with Claude Code