feat(web): finish RE 5000PBR lesson video and fix non-ASCII GLB import

- Add 11:07 Chinese-narrated lesson video, VTT, poster and 13 chapter screenshots.
- Regenerate 20-render WebGL2 matrix and 15 operation captures on RTX 4060.
- Fix WASM staging for non-ASCII import filenames (猴头.glb); rebuild web_engine.
- Harden lesson video recording pipeline; fix stale lesson-link E2E selector.
- Add RE PBR derived libraries, lesson page, evidence and status report.

Co-Authored-By: Claude Code <noreply@anthropic.com>

web/protocol/render-assets.ts

@@ -9,7 +9,7 @@ export const MAX_GPU_TEXTURE_DIMENSION = 16_384;
 export const MAX_GPU_TEXTURE_ASSETS = 256;
 export const MAX_UDIM_TILES = 64;
 
-export type GPUTextureUsage = "BASE_COLOR" | "NORMAL" | "METALLIC" | "ROUGHNESS" | "EMISSIVE" | "ALPHA" | "BUMP" | "DATA" | "ENVIRONMENT" | "UDIM_TILE";
+export type GPUTextureUsage = "BASE_COLOR" | "NORMAL" | "METALLIC" | "ROUGHNESS" | "EMISSIVE" | "ALPHA" | "BUMP" | "HEIGHT" | "DATA" | "ENVIRONMENT" | "UDIM_TILE";
 export type GPUTextureColorSpace = "SRGB" | "NON_COLOR" | "LINEAR";
 
 export interface GPUTextureAssetRequest {
@@ -108,22 +108,35 @@ function materialUsages(materials: MaterialIR[]): Map<string, Set<GPUTextureUsag
     usages.set(imageId, current);
   };
   for (const material of materials) {
-    if (material.normalImageId) add(material.normalImageId, "NORMAL");
-    for (const binding of material.textureBindings ?? []) add(binding.imageId, binding.usage === "EMISSION" ? "EMISSIVE" : binding.usage);
+    const bound = new Set<string>();
+    if (material.normalImageId) {
+      bound.add(material.normalImageId);
+      add(material.normalImageId, "NORMAL");
+    }
+    for (const binding of material.textureBindings ?? []) {
+      bound.add(binding.imageId);
+      add(binding.imageId, binding.usage === "EMISSION" ? "EMISSIVE" : binding.usage);
+    }
     for (const imageId of material.imageIds ?? []) {
-      if (!material.textureBindings?.some((binding) => binding.imageId === imageId)) add(imageId, imageId === material.normalImageId ? "NORMAL" : "BASE_COLOR");
+      if (bound.has(imageId)) continue;
+      add(imageId, imageId === material.normalImageId ? "NORMAL" : "BASE_COLOR");
     }
     for (const node of material.nodes ?? []) {
-      if (node.type === "IMAGE_TEXTURE" && node.imageId) add(node.imageId, node.imageId === material.normalImageId ? "NORMAL" : "BASE_COLOR");
+      if (node.type === "IMAGE_TEXTURE" && node.imageId && !bound.has(node.imageId)) {
+        add(node.imageId, node.imageId === material.normalImageId ? "NORMAL" : "BASE_COLOR");
+      }
     }
   }
   return usages;
 }
 
 function requestForImage(image: ImageIR, usage: GPUTextureUsage): GPUTextureAssetRequest[] {
-  const colorSpace: GPUTextureColorSpace = image.colorSpace ?? (usage === "BASE_COLOR" || usage === "EMISSIVE" ? "SRGB" : usage === "ENVIRONMENT" ? "LINEAR" : "NON_COLOR");
-  if (image.tiles?.length) {
-    return image.tiles.filter((tile) => tile.packed).map((tile) => ({
+  const colorSpace: GPUTextureColorSpace = usage === "HEIGHT"
+    ? "NON_COLOR"
+    : image.colorSpace ?? (usage === "BASE_COLOR" || usage === "EMISSIVE" ? "SRGB" : usage === "ENVIRONMENT" ? "LINEAR" : "NON_COLOR");
+  const tiles = image.tiles;
+  if (tiles && tiles.length > 1) {
+    return tiles.filter((tile) => tile.packed).map((tile) => ({
       assetId: tile.assetId,
       imageId: image.id,
       mimeType: imageMimeType(tile.mimeType),
@@ -134,6 +147,19 @@ function requestForImage(image: ImageIR, usage: GPUTextureUsage): GPUTextureAsse
       tileNumber: tile.number,
     }));
   }
+  if (tiles && tiles.length === 1) {
+    const tile = tiles[0];
+    if (!tile.packed) return [];
+    return [{
+      assetId: tile.assetId,
+      imageId: image.id,
+      mimeType: imageMimeType(tile.mimeType),
+      width: image.width || tile.width,
+      height: image.height || tile.height,
+      usage,
+      colorSpace,
+    }];
+  }
   if (!image.packed) return [];
   return [{
     assetId: image.assetId,
@@ -162,6 +188,26 @@ export function collectGPUTextureAssetRequests(snapshot: SceneSnapshotIR): GPUTe
   return [...unique.values()];
 }
 
+/**
+ * Number of GPU texture assets the packed-asset fallback will produce. This
+ * includes images that have no MaterialTextureBinding yet (the App adds a
+ * BASE_COLOR/ENVIRONMENT fallback for them) so readiness cannot release early.
+ */
+export function expectedGPUTextureAssetCount(snapshot: SceneSnapshotIR): number {
+  const requests = collectGPUTextureAssetRequests(snapshot);
+  const represented = new Set(requests.map((request) => request.assetId));
+  let count = requests.length;
+  for (const image of snapshot.images) {
+    if (image.tiles?.length) {
+      for (const tile of image.tiles) if (tile.packed && !represented.has(tile.assetId)) count += 1;
+    }
+    else if (image.packed && !represented.has(image.assetId)) {
+      count += 1;
+    }
+  }
+  return count;
+}
+
 export function createUDIMManifest(image: ImageIR): UDIMManifest {
   if (image.sourceKind !== "TILED" || !image.tiles?.length || image.tiles.length > MAX_UDIM_TILES) {
     throw new RenderAssetValidationError("UDIM_MANIFEST_INVALID", `Image ${image.id} does not have a bounded UDIM tile set`);