docs(game-data): correct the v3.0.0 migration changelog

[ChessMess]

Found while reviewing what PR #58 would publish. ultimatedarktowerdata 2.2.0 →
3.0.0 is a genuine major that removes the whole gameContent namespace, so
.changeset/hero-record-merge.md becomes the published CHANGELOG — and
packages/game-data ships CHANGELOG.md in its files list, so this text is
the migration doc external consumers actually receive.

1. The hero count was wrong

Through v2 the same 14 heroes existed twice

heroes.ts has 14 rows, but only 10 carry bannerAction, and the removed
gameContent.ts held 10 hero sheets. The same document already says "all 10
hero sheets transferred byte-identical" and "four heroes genuinely have no
sheet" (the unreleased Expeditions heroes).

A reader hitting "14 existed twice" and then "four have no sheet" concludes data
was dropped in the merge. Nothing was. Corrected to "10 of the 14".

2. Adversary → Foe was an unremarked type collapse

The migration table maps three types onto two in a single cell:

Removed	Use instead
gameContent.Foe / .Adversary / .Companion	Foe / CompanionCard

Nothing says adversaries are now modelled as Foe — ADVERSARY_ROSTER is a
readonly Foe[] and ALL_FOES is [...FOES, ...ADVERSARY_ROSTER]. A consumer
with let a: gameContent.Adversary can't guess Foe from that row. Added a
short paragraph after the table.

3. Two stale source comments from the same removal

• boxInventory.ts — "Gameplay content lives in gameContent.ts" (that file is
  deleted).
• companionCards.ts — "gameContent.COMPANIONS holds the same 10 quest
  companions", present tense.

What I verified but did not change

Every replacement name in the migration table resolves against the real v3
export surface (HERO_BY_NAME, HERO_BY_ID, HEROES, FOES,
ADVERSARY_ROSTER, COMPANION_CARDS, KINGDOM_VIRTUES, kingdomVirtues,
KingdomDirection, Virtue, Hero, Foe, CompanionCard, ContentSource) —
no dangling references. gameContent was a named export of ., never a
subpath, so the import { gameContent } diff has the right shape. Nothing in
the repo still imports it, and virtues.test.ts asserts it stays gone.

Verification

pnpm run ci passes (exit 0). pnpm --filter ultimatedarktowerdata test — 326
passed / 13 files. pnpm changeset status still resolves ultimatedarktowerdata
to major.

Merging this regenerates the "Version Packages" PR (#58) with the corrected text.