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>

tools/web/deployment-http-server.mjs

@@ -42,9 +42,15 @@ function resolvedFile(root, pathname) {
   return filePath;
 }
 
-function strongEtag(filePath) {
+const etagCache = new Map();
+function strongEtag(filePath, stat) {
+  const key = path.resolve(filePath);
+  const cached = etagCache.get(key);
+  if (cached && cached.size === stat.size && cached.mtimeMs === stat.mtimeMs) return cached.etag;
   const hash = crypto.createHash("sha256").update(fs.readFileSync(filePath)).digest("hex");
-  return `"sha256-${hash}"`;
+  const etag = `"sha256-${hash}"`;
+  etagCache.set(key, { size: stat.size, mtimeMs: stat.mtimeMs, etag });
+  return etag;
 }
 
 function matchesIfNoneMatch(value, etag) {
@@ -121,7 +127,7 @@ export function createDeploymentHttpServer({ root, contract = loadDeploymentCont
     const extension = path.extname(filePath).toLowerCase();
     if (expectedAuthorization) { headers["Cache-Control"] = "private, no-store"; headers.Vary = "Authorization"; }
     const rangeEnabled = contract.rangeRequests.extensions.includes(extension);
-    const etag = strongEtag(filePath);
+    const etag = strongEtag(filePath, stat);
     headers.ETag = etag;
     if (rangeEnabled) headers["Accept-Ranges"] = contract.rangeRequests.unit;
     if (matchesIfNoneMatch(request.headers["if-none-match"], etag)) {