feedback5 WE2: remove the kits/tier1-6.js re-export shims and shared/standIn.js diyRecord (#5)

Nothing but tests imported them: kits_t3 / kits_alt_t3 / kits_t4 / kits_t5 read
kits/index.js TIER_KITS, playtest5_elements / playtest6-combat / facing the real modules,
simServe checks /sim/content/kits/index.js; test/backups.test.js composes the prototypes
through shared/diy.js diyRecordOf at their locked selection. check:imports passes.
Docs: kits/README.md, DATA.md. Golden: no scenario moved.

test/content/kits_t3.test.js

@@ -5,9 +5,11 @@ import assert from 'node:assert/strict';
 import { makeBattle, enemyRec, checkInvariants } from '../helpers/battleHarness.js';
 import { getDefaultSource } from '../../server/sim/simdata.js';
 import { effectiveProfile } from '../../server/sim/ai.js';
-import KITS from '../../server/sim/content/kits/tier3.js';
+import { TIER_KITS } from '../../server/sim/content/kits/index.js';
 import { COLS } from '../../server/sim/constants.js';
 
+const KITS = TIER_KITS[2];
+
 const ds = getDefaultSource();
 const D = (id) => ds.getChess(id);
 const BB = (id) => D(id).skill.bb;