feedback1e WQ: healers that block keep healing (E2 not reproduced, locked by tests)

A community report said a medic blocking a roaming boss in a 炎 build stops
healing and strikes the boss, its 强力击-type skill included. The real sim
does not do that: every pure healer (医师 / 群愈师 / 疗养师 / 链愈师 / 行医,
the map characters, normal and elite, every skill) blocking an enemy keeps
healing and never targets it, under every bond as a member, with every
equipment item and on every boss / hidden field (卢西恩 and its phantom,
the 剑 / 锤). Official: PRTS 卫戍协议/帮助 "对于医疗干员（咒愈师分支除外），
攻击目标为需要治疗的单位". The only damage a pure healer deals is a bond's
own effect by its text (卡西米尔's pulse while blocking).

No behaviour change: the rule is spelled out in SIM.md and ai.js
acquireTargets, and test/sim/feedback1e-healers.test.js locks it (the
reported 炎 boss round, every healer x bond, items, heal-mode skills of
古米 / 塞雷娅 / 波登可, 咒愈师 and 吟游者, every boss template).

server/sim/ai.js

@@ -102,6 +102,9 @@ export function enforceBlockCapacity(b, u) {
 
 /** Collect targets for an ally with profile `prof`. */
 export function acquireTargets(b, u, prof) {
+  // a heal attack (医师 / 群愈师 / 疗养师 / 链愈师 / 行医, a skill attack turned into a heal) selects injured allies only,
+  // never the enemies its unit blocks — a blocking healer keeps healing: PRTS 卫戍协议/帮助 "对于医疗干员（咒愈师分支除外），
+  // 攻击目标为需要治疗的单位" (the blocked-first rule below is for attackers of enemies; community feedback after 0.1.0, E2)
   if (prof.heal && prof.dmgType === 'heal') {
     let cands = b.injuredAlliesInKeys(u.rangeKeys, u, !!prof.heal.elementHealRatio);
     // a heal restricted to allies at or below an HP ratio (塞雷娅 S1 急救 "血量小于等于一半")