feat(api): auditable map revisions with deltas + periodic snapshots (#12)

[Aduersarius]

Summary

Implements OpenAO #12 with the issue's recommended deltas + periodic snapshots design (snapshot every 20 revisions), plus undo/redo, arbitrary rollback, readable diffs, and requiresRepublish when undoing a publish.

Closes #12

Design

• New tables game_map_revisions / game_map_revision_heads
• Each paint/clear/publish/discard/revert appends a compact tile delta (before/after per changed coord)
• Every 20th revision also stores a full snapshot so reconstruction stays bounded
• undo inverts the current head delta and sets requiresRepublish if the undone op was publish (published world is not silently changed without an explicit republish)
• redo / rollback / diff rebuild via nearest snapshot + forward deltas

Admin API

• GET /admin/game-data/maps/:mapNum/revisions
• GET /admin/game-data/maps/:mapNum/revisions/diff?from=&to=
• GET /admin/game-data/maps/:mapNum/revisions/:revisionId
• POST /admin/game-data/maps/:mapNum/undo
• POST /admin/game-data/maps/:mapNum/redo
• POST /admin/game-data/maps/:mapNum/rollback/:revisionId

Differentiation vs #73

#73 stores full before/after snapshots on every operation inside worldBuilder.ts. This PR follows the issue suggestion: lightweight deltas + periodic snapshots, isolated in gameMapRevisions.ts, so undo is natural and storage stays bounded for long edit sessions.

Test plan

• Unit tests for delta round-trip / invert-undo / publish draft→published visibility (api/src/tests/mapRevisions.unit.test.ts)
• Apply schema migration locally; paint → list revisions → undo → redo → rollback
• Undo after publish returns requiresRepublish: true and does not leave draft as silently live

GrantFox OpenAO bounty submission for #12.

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