Fix correctness bugs in TextureManager and image worker

[chiefcll]

Summary

Reviewed CoreTextureManager, ImageTexture, and ImageWorker for bugs and lower-risk issues, and fixed them in this PR. Larger optimizations (in-flight dedup, parallel getTextureData in processSome, lazy resolveDefaults on cache miss, replacing XHR with fetch+AbortController) are intentionally not included here and tracked separately.

What changed

ImageWorker

• Fixed a dead/tautological supportsOptionsCreateImageBitmap === false && supportsOptionsCreateImageBitmap === false branch that caused modern browsers to silently fall through to the no-options createImageBitmap(blob) path. The fallback now requires both options and full support to be false.
• Worker now resolves with the computed withAlphaChannel instead of echoing the raw input — previously the worker path returned null/undefined for PNGs while the main-thread path returned true, leading to inconsistent GL uploads.
• withAlphaChannel now treats null the same as undefined, matching the main thread's nullish-coalesce behavior.
• getImage now rejects when no worker is available instead of leaving the promise hanging.
• Wired worker.onerror / worker.onmessageerror: a crashed worker now rejects all outstanding pending requests rather than hanging the entire load pipeline.
• Worker-script blob URL is revoked after workers spawn.
• let minLoad = 99 → Infinity so we always pick the genuinely least-loaded worker.
• Removed unused imageWorkersEnabled field.

ImageTexture

• Object URL created from a Blob in loadImageFallback is now revoked on both onload and onerror, fixing a per-image leak on the non-createImageBitmap fallback path.
• makeCacheKey now inserts delimiters between sx/sy/sw/sh so values like (sx=1, sy=23) and (sx=12, sy=3) no longer collide.
• loadImage computes isBase64Image(src) once.

CoreTextureManager

• New TEXTURE_UPLOAD_FAILED error code; upload failures no longer masquerade as TEXTURE_DATA_NULL, and the underlying error message is propagated.
• Removed misleading coreContext !== null check around loadCtxTexture() (return type is non-nullable; the check shadowed an actual NPE risk that didn't exist).
• processSome skips failed/freed textures pulled from the queue instead of wasting a fetch/decode on dead entries.
• enqueueUploadTexture rejects failed/freed textures so the queue never holds dead entries in the first place.
• When initialization completes, any textures enqueued pre-init are drained immediately instead of sitting until the next frame tick happens to call processSome.
• Fixed typo in the no-image-worker warning string.

TextureError

• Added TEXTURE_UPLOAD_FAILED to the enum and default-messages map.

Why this matters

The two most impactful items: the duplicate-variable bug was silently disabling the optimal createImageBitmap code path on every modern browser, and the worker-crash / no-worker cases could hang load promises indefinitely. The rest are smaller correctness fixes and resource leaks.

Test plan

• Existing visual-regression tests pass
• Existing unit tests pass (pnpm test)
• Manually verify image loading on a representative scene
• Verify failed-image case surfaces TEXTURE_UPLOAD_FAILED with a meaningful message instead of TEXTURE_DATA_NULL
• Verify a deliberately bad URL no longer hangs (rejects via worker error path)

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