feedback5 WY: 拟态物质 with 2 copies owned and none left in the pool gives nothing instead of a random same-bond operator (GitHub #207)

The item text 「若已拥有至少2名该初始干员，则再获得1名该初始干员；否则随机获得1名同盟约初始干员」: the 否则 is the
case of fewer than 2 owned. builtinMeta's use_equip_reward_char_chess returned only when grantChess(base) gave a piece,
so an elite 溯光星源 plus 2 normal copies (all 5 Ⅵ阶 copies) fell through to the same-bond roll (白面鸮 in the report's
seed). Now with 2 owned it asks for the 3rd and stops; the item is still consumed. The bots' carrier choice
(itemTarget) skips 2 copies whose pool is out.

Tests: test/content/items.test.js (the report with the normal and golden item; 2 copies with the pool drained; 2 copies
with copies left still merge), test/match/bot-smarter.test.js (no carrier on a pair whose pool is out); both fail
without the fix. Docs: META built-ins and bot items, research 04 / 06, DESIGN §25.13.1.
Golden unchanged.

test/match/bot-smarter.test.js

@@ -108,6 +108,10 @@ test('items: 信标 on a bench single; both 博士投影 on a normal operator ev
   // 拟态物质 (a third copy when two are owned): the pair
   const mimic = itemTarget(m, ps, giveItem(m, ps, 'chess_item_5_05_e_a'));
   assert.ok(mimic && [pairA.uid, pairB.uid].includes(mimic.uid), '拟态物质 on the pair');
+  // …but not once the pool has no third copy: the item would give nothing (GitHub #207)
+  m.pool.take(pairId, m.pool.left(pairId));
+  const mimic2 = itemTarget(m, ps, giveItem(m, ps, 'chess_item_5_05_e_a'));
+  assert.ok(mimic2 && ![pairA.uid, pairB.uid].includes(mimic2.uid), '拟态物质 not on a pair whose pool is out');
   m.dispose();
 });