docs(tdd): make test-driven-development ecosystem-neutral (#404 Phase 1)

- SKILL.md gains a 'Discover the Stack First' step: identify the
  language, build system, checked-in wrappers, test framework, and
  documented commands before choosing any test command, and run the
  repository's own focused/full-suite commands throughout the loop
- verification checklist no longer hardcodes 'npm test'; red flag added
  for reaching for a default test command without checking the repo
- references/testing-patterns.md relabeled in place as JavaScript/
  TypeScript examples illustrating the universal principles (no
  relocation, per the #361/#236 sequencing agreed in the issue)
- new behavioral eval: a Python/unittest fixture verifying the skill
  adapts to non-npm repository tooling

references/testing-patterns.md

@@ -1,6 +1,6 @@
-# Testing Patterns Reference
+# Testing Patterns Reference (JavaScript/TypeScript)
 
-Quick reference for common testing patterns across the stack. Use alongside the `test-driven-development` skill.
+Quick reference of JavaScript/TypeScript testing patterns — Jest, React Testing Library, Supertest, and Playwright — illustrating the universal principles from the `test-driven-development` skill. The principles (Arrange-Act-Assert, naming, mock discipline, anti-patterns) apply in any ecosystem; the syntax and tooling shown here are JS/TS-specific. In another stack, follow the same principles with the repository's own test framework and commands.
 
 ## Table of Contents