refactor: rename core-public -> engine-public; fold helpers in; drop shared

Tighten the package model around the determinism invariant: everything the
engine imports must itself be deterministic.

- Rename core-public -> engine-public (package, dir, `engine-public/*` alias,
  all 118 import sites). It is the deterministic public surface the engine
  depends on and that client/server also use.
- Move the pure formatting helpers (renderNumber/renderTroops) from shared
  into engine-public/format — the engine uses them and they're deterministic.
- Drop the now-empty shared package (and its alias). `shared` was intended for
  client/server-shared, engine-forbidden code; there is none yet, so it is
  removed and can be re-added when such code appears.

Final graph: engine-public (leaf) <- engine <- {client, server};
client/server also -> engine-public.

Verified: tsc clean; 1364 + 65 tests pass; prod build succeeds; engine-public
is a leaf; engine has no client/server imports. Lockfile regenerated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/server/Archive.test.ts

@@ -20,8 +20,8 @@ vi.mock("server/Logger", () => ({
   },
 }));
 
-vi.mock("core-public/Schemas", async () => {
-  const actual = (await vi.importActual("core-public/Schemas")) as any;
+vi.mock("engine-public/Schemas", async () => {
+  const actual = (await vi.importActual("engine-public/Schemas")) as any;
   return {
     ...actual,
     GameRecordSchema: {
@@ -31,7 +31,7 @@ vi.mock("core-public/Schemas", async () => {
 });
 
 import { GameType } from "engine/game/Game";
-import type { GameRecord } from "core-public/Schemas";
+import type { GameRecord } from "engine-public/Schemas";
 import { archive } from "server/Archive";
 
 function buildRecord(gameType: GameType, flag: string | undefined): GameRecord {

tests/server/GameLifecycle.test.ts

@@ -1,7 +1,7 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
-vi.mock("core-public/Schemas", async () => {
-  const actual = (await vi.importActual("core-public/Schemas")) as any;
+vi.mock("engine-public/Schemas", async () => {
+  const actual = (await vi.importActual("engine-public/Schemas")) as any;
   return {
     ...actual,
     GameStartInfoSchema: {

tests/server/KickPlayerAuthorization.test.ts

@@ -1,7 +1,7 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
-vi.mock("core-public/Schemas", async () => {
-  const actual = (await vi.importActual("core-public/Schemas")) as any;
+vi.mock("engine-public/Schemas", async () => {
+  const actual = (await vi.importActual("engine-public/Schemas")) as any;
   return {
     ...actual,
     GameStartInfoSchema: {