feedback1 integrate: DESIGN §21.21-§21.25 and CHANGELOG for batch 6 and the PR-credited fixes

DESIGN maps F1-F5 in the §21 intro, adds the hammer-per-deployment row (user 2026-10-03) to
§21.20 with the batch's official rules and [ASSUMED] items, and rewrites the normative lines:
§3 fenced tiles, §5.3 liftoff, §5.4 fatal / ignoreSelect / redeploy, §5.5 bodies, blocking and
enemy selection, §6.4 onBuy and the item snapshot, §8.2 down row/col, §18.3, §19.7. CHANGELOG
0.1.1, SIM, DATA and PLAYING follow; docs-consistency checks them against the code.

docs/SIM.md

@@ -665,7 +665,7 @@ registration order. `battle.off(handle)` / `battle.off(name, fn)` / `battle.offO
 | `elementHit` | `{ source, target, dmg }` | before a gauge fill (`dmg.type === 'element'`); mutate `dmg.amount`/`dmg.mul`, set `dmg.cancel` |
 | `damaged` | `{ source, target, amount, type, dmg, credit }` | after application (`amount` may be 0 when shielded); element fills too (with their source); 无来源: `source` null, `credit` set |
 | `heal` | `{ source, target, amount, opts }` | mutable `amount` |
-| `fatal` | `{ unit, source, credit, dmg, amount, prevented }` | HP would reach 0 — set `prevented` (substitutes, kit savers, 不死 / 复活 items, 埃芒加德; 不屈 is a `death` hook). Fired by every HP loss of a unit without a boss pool — hits of any type, element bursts, 无来源 damage, `loseHp` 流失. Order: kits' own savers (10 … −60) → items' 不死 (坚固维式重锤, `PRIO_REVIVE` −100; substitutes −100) → items' 复活 (M3茧甲, `PRIO_RESPAWN` −101: PRTS "复活" acts on a knock-out, which a 不死 prevents) → 埃芒加德 (−110) |
+| `fatal` | `{ unit, source, credit, dmg, amount, prevented }` | HP would reach 0 — set `prevented` (substitutes, kit savers, 不死 / 复活 items, 埃芒加德; 不屈 is a `death` hook). Fired by every HP loss of a unit without a boss pool — hits of any type, element bursts, 无来源 damage, `loseHp` 流失. Order: kits' own savers (10 … −60) → items' 不死 (坚固维式重锤 — once per deployment: the carrier's own non-initial `deploy` re-arms it, DESIGN §21.21 — `PRIO_REVIVE` −100; substitutes −100) → items' 复活 (M3茧甲, `PRIO_RESPAWN` −101: PRTS "复活" acts on a knock-out, which a 不死 prevents) → 埃芒加德 (−110) |
 | `kill` | `{ killer, victim }` | victim HP reached 0 (a handler may revive by restoring HP) |
 | `death` | `{ unit, reason:'killed'|'leak'|'retreat'|'merchant'|'expired'|'forcedExit', killer }` | unit removed (`'forcedExit'`: an operator entering 联防 knocked out, §1.1) |
 | `skillStart` / `skillEnd` | `{ unit, skill, reason }` | mutate `skill.ammoLeft` / `skill.timeLeft` in skillStart |