test(comments): no plan code lands in the code again

planCodes.contract.test.ts scans every tracked text file and every new one not yet added (comments,
docstrings, test titles, lint messages alike) for an epic or roadmap code (`E28`, `E9.5`, `R14`) and
for a sprint or review round cited on its own (`(S6)`, `S3e2`, `round 4`, `deep-review`). Not
`E2E`, not a ruff rule family (`E4/E7/E9`), not a TV episode (`S2 · E5`, a test episode titled
"E1"), not `S3h` (the media-card decision docs/DESIGN.md is headed by). Markdown and the Alembic
migrations keep their history and are not scanned.

One sweep test rather than an ESLint rule plus a ruff one: the codes sat in Python, TS, CSS, shell,
TOML, YAML and lint messages, and no single linter reads all of them. Seen red on a planted
backend/app file (all three plan-code lines named, its allowed line not).

audit_metrics.py counts epic codes by the same definition (it used to miss `E9.5` and `R6`), and
CLAUDE.md's "comment the why" rule names the test.

CLAUDE.md

@@ -125,7 +125,8 @@ controls (`ui/Input`, `Checkbox`, `Slider`, …), glass surfaces (`SURFACE.*`),
   "no results". Reads degrade honestly; writes are conditional (`UPDATE … WHERE status='running'`).
 - **i18n parity.** HU/EN, zero key drift. Every user-facing string is translated.
 - **Comment the "why", keep it current.** This codebase uses comments as its architecture doc; a stale
-  "why" is a liability, so update it when the behavior changes.
+  "why" is a liability, so update it when the behavior changes. Say the why itself, never the plan
+  step that produced it: no epic, sprint or review-round ids in the code (`planCodes.contract.test.ts`).
 
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