feedback5 WD: the sim fields a 补位 stand-in — getChess(id, { standIn: true }) over data/backups.json, PlayerBattleInput standIn: true, kits by the stand-in's charId (never the replaced operator's), kits/ops/standin-<codename>.js registry, harness standIn

- simdata: DataSource keeps `backups` (rawBackups follows the fallback chain); getStandIn = shared/standIn.js
  standInRecord normalised (the chess's ids / bonds / 特质 / tier, the stand-in's body, def.standInFor); a PRESET / DIY
  chess or a source without backups fields itself; the per-battle view maps id-only lookups.
- spec.js keeps `standIn` only when exactly true (never on a token); Battle passes it to getChess; syncUnitLoadout
  carries it; UnitInfo `standInFor`.
- content/index.js kitOf: a stand-in's kit is KITS[def.charId] only; no default skill (a stand-in kit writes `skills`);
  without a kit the generic kit plus genericTalents. kits/index.js STANDIN_KIT_FILES / STANDIN_KITS, merged after the
  tier groups (old keys keep their order; golden unchanged).
- server/data.js and tools/setup.mjs expect backups.json.
- test/content/standin.test.js: the plumbing and the eight 预备干员 on all 28 chess records they replace.

server/data.js

@@ -2,7 +2,7 @@
 //
 // Every `*.json` file in the data directory becomes a top-level key named after its basename
 // (config, chess, bonds, garrisons, items, bands, effects, choices, enemies, factions, waves, stages,
-// bosses, tokens, assets, …). The result is deep-frozen so no module can mutate shared data by accident.
+// bosses, tokens, assets, backups, …). The result is deep-frozen so no module can mutate shared data by accident.
 // Missing or unparsable files are tolerated with a warning (data is generated in parallel with the
 // server); consumers must cope with an absent key.
 //
@@ -26,7 +26,7 @@ export const DATA_DIR = path.join(ROOT, 'data');
 /** Files the game expects (a warning lists the missing ones). */
 export const DATA_FILES = Object.freeze([
   'config', 'chess', 'bonds', 'garrisons', 'items', 'bands', 'effects', 'choices',
-  'enemies', 'factions', 'waves', 'stages', 'bosses', 'tokens', 'assets',
+  'enemies', 'factions', 'waves', 'stages', 'bosses', 'tokens', 'assets', 'backups',
 ]);
 
 /**