docs(testing): scope the test-location rule — subsystem packages keep their suite in-package

[anikinsasha]

TestingDoctrine rule 2 maps every test into the repo-root test/ tree, and the anti-patterns list bans co-location without qualification. That is right for the repo-root surface (hooks, skills, single-file tools) but leaves one shipped class with no home in the rule: self-contained subsystem packages — tool directories with their own package.json, in the current payload LIFEOS/TOOLS/TokenXray/ and LIFEOS/TOOLS/llcli/. A package with its own dependencies and lifecycle is the unit that travels; routing its suite into the repo-root tree strands the tests whenever the package is developed, vendored, or deployed on its own.

Changes (docs only, no behavior change):

• Rule 2 gains a Subsystem-package clause: a directory-tool with its own package.json keeps its suite in-package at <tool>/test/ with a package.json test script — the suite travels with the deployable package. The parallel repo-root test/ tree continues to govern the repo-root surface.
• The co-location anti-pattern row is scoped to match (repo-root surface only; subsystem packages keep in-package suites per Rule 2). A package-local test/ directory is the parallel-tree pattern at package scope, not co-location — co-location means a test file next to its source file.

Deliberately not touched: no test tree or harness is added (that packaging question is #1550's, whose resolution this clause is consistent with — the clause governs where tests live when they exist); no bunfig or code changes; rules 1 and 3–11 unchanged. The corpus coverage rule (every hook/skill/tool surface gets at least one test file) loses nothing — a repo-root bun test walk still reaches in-package suites.

We run this split on our install: two subsystem tools keep their suites in-package (a 14-file suite behind a bare bun test script; a second package whose script scopes unit tests apart from live-integration runners), run per-package, with the packages' deploy scripts shipping test/ alongside the code — tests traveling with the package is exactly what the clause writes down.