fix(web): make first wasm load work on remote deployment

- Correct engine-manifest single wasm SHA and reuse cache for verification.
- Remove duplicate main-thread wasm fetch; raise init timeout to 300s.
- Record production deployment details and verification evidence.

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

web/app/public/engine-manifest.json

@@ -21,7 +21,7 @@
         "wasm": {
           "fileName": "web_engine.wasm",
           "url": "/vendor/blender/web_engine.wasm",
-          "sha256": "551a86b11ec0c2a8d2097e9f6aa80beda1a041c46c437ead7eb98db97fcd47d8"
+          "sha256": "31550b374cc0127c9b5468cebe65be37b8558c1604a28e99ec73a34be96c13f3"
         }
       }
     },