fix(merge): pair Ruby tests with production files by path

[viktorianer]

Summary

Since #689 the tested_by linker classifies Ruby test files, but production_candidates() has no Ruby branch. The path-convention pass therefore never pairs a Ruby test the analyzer did not link. This adds that branch for Rails and gem layouts.

• test/<tail>/x_test.rb and spec/<tail>/x_spec.rb try app/<tail>/x.rb, then lib/<tail>/x.rb, then <tail>/x.rb, so test/lib/foo_test.rb resolves to lib/foo.rb.
• test_x.rb (classic Minitest in gems) follows the same mapping.
• A path prefix before the first test/ or spec/ segment is kept, so engines/billing/spec/models/invoice_spec.rb resolves to engines/billing/app/models/invoice.rb.
• A test outside a test tree, for example lib/parser_test.rb, tries its sibling only. Inside a test tree, the sibling is skipped, so a support file such as test/support/user.rb is never taken for production code.
• test_helper, spec_helper and rails_helper produce no candidates. Otherwise test_helper.rb would pair with an unrelated lib/helper.rb.

Linked issue(s)

Refs #646, #689

How I tested this

• New unit tests cover the Rails Minitest, Rails RSpec, gem, test/lib, engine-prefix and sibling layouts, plus the helper and support-file exclusions. Two link_tests cases cover the end-to-end result. With the new branch reverted, 7 of them fail.

• Ran the candidate function over the file list of a large private Rails application. 1,526 of 2,185 Ruby test files paired, and every pairing landed under app/ or lib/. The unpaired ones are mostly request and integration specs, which have no single production file.

• pnpm lint

• pnpm --filter @understand-anything/core test (run through pnpm test)

• pnpm test, plus python -m unittest tests.skill.understand.test_merge_batch_graphs tests.skill.understand.test_merge_subdomain_graphs tests.skill.knowledge.test_parse_knowledge_base

• Manual smoke test (described above)

Versioning

• Version bumped in all five manifests, OR
• N/A — internal/docs-only change

Bumped 2.9.7 → 2.9.8 in the six files listed in CLAUDE.md.

🤖 Generated with Claude Code

https://claude.ai/code/session_011d1u3dqu58uR21urdNqri9