fix(extension): resolve transformer wasm runtime fetch failures

[janitrbob]

Summary

• restore ORT wasm runtime path resolution to Hugging Face runtime assets for builtin and downloaded HF runs
• persist per-run runtime_wasm_base_url and reuse it during inference
• improve transformer fetch/session errors to include failing URL/label and configured wasmPaths

Why

The extension package does not include the ORT wasm binary, so forcing local wasm paths causes runtime "Failed to fetch" during transformer inference.

Validation

• npm run extension:typecheck
• npm run format:check
• npx playwright test extension/tests/transformer-smoke.spec.ts --reporter=line (skips in no-DISPLAY env)

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