fix: harden chest patch, battle calc loading, and double-injection

[timzatko]

Why

Three intermittent runtime errors reported in production:

1. Chests.init | Unexpected token '}' — the chest tracker rewrites ItemUse.doIt by string-inserting a trackChest call before the item_used signal. The anchor lookup used a single-quote-only indexOf with no "not found" guard. When indexOf returned -1 (anchor absent, e.g. a minified build emitting the signal with double quotes), the substr math collapsed the body to TW_Calc.trackChest(itemId,res);} and eval threw a misleading Unexpected token '}'.

2. "Battle calc core script is not loaded" — BattleCalc.init fired a single fire-and-forget $.getScript with no error handling, so a transient/failed fetch left the calc unavailable for the whole session, with only "refresh the game" as recovery.

3. Initializer.registerApi | given parameter ('tw-calc') is already registered! — the script could be injected more than once into the same page (re-injection or a same-origin iframe), so bootstrap ran twice and TheWestApi.register threw on the second run. The register collision was the visible symptom of everything initializing twice.

What

Chests

• Quote-agnostic anchor via regex (/EventHandler\.signal\(['"]item_used['"]/) so double-quoted builds patch correctly.
• Guard the not-found case: throw a clear, trackable error instead of building broken code from a -1 position.

Battle calc

• Retry the core-script load up to 3 times with a backoff, logging each failure via Logger.
• Guard against concurrent/duplicate loads with a loading flag.
• When a view finds the calc unavailable, kick off a background reload so reopening the window recovers it without a full game refresh.

Double injection

• Extract the injection logic into src/inject.ts and skip bootstrapping when window.TW_Calc is already set, making injection idempotent (fixes the root cause, not just the API-register symptom).

Tests

New specs for all three areas (none existed before) — 14 new tests, full suite green (npm test → 18/18). tsc, eslint, and npm run build:dev all clean.

• chests.spec.ts: single/double-quote anchor patching + missing-anchor error path.
• battle-calc.spec.ts: load on init, retry-with-logging, in-progress/already-available guards, getInstance behavior.
• inject.spec.ts: game-ready and already-injected guards (driven with jasmine's clock).

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