docs: retire the test review plan, keep its durable findings

Every item in TEST_REVIEW_PLAN.md is done or decided, so the working
document goes as its own header instructed. What outlives it moves to
where a later reviewer will actually look:

- TESTS.md gains the -coverpkg command and the 84.4% baseline (per-package
  figures understate the suite), design principle 9 (redundancy is judged
  by comparing coverage profiles, and identical coverage alone is not
  grounds for deletion), a table of the look-alike tests that are kept
  with the reason each survives, and the list of functions deliberately
  at 0%.
- STANDARDS.md's "Intentional behavior" section points at both lists, so
  the mechanism REVIEW.md describes still reaches them.

Dropped as spent: the per-item checklists, the suggested order, and the
model-selection table.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/STANDARDS.md

@@ -66,6 +66,10 @@ change to their shape has to stay compatible on its own.
 - **History tab is session-only.** `JobRuntime.Logs` exists only in memory for the
   current process. Log files on disk feed aggregate statistics via `SeedStats`
   only. See [ARCHITECTURE.md](ARCHITECTURE.md).
+- Several tests share a coverage profile with another test on purpose, and a few
+  functions sit at 0% on purpose. Both lists live in
+  [TESTS.md](TESTS.md) — check them before reporting a test as redundant or a
+  coverage gap as an oversight.
 
 ## Out of scope