QVAC-18995 feat[api]: bump transcription-whispercpp to 0.9.0 and surface backend/GPU stats

[ishanvohra2]

🎯 What problem does this PR solve?

• The SDK was pinned to @qvac/transcription-whispercpp@^0.8.0, missing the 0.9.0 release.
• whisper.cpp 0.9.0 adds backend/GPU runtime stats (active device class, GPU backend family, GPU memory) that the SDK did not expose to consumers.

📝 How does it solve it?

• Bump @qvac/transcription-whispercpp ^0.8.0 → ^0.9.0.
• Thread the four new runtimeStats fields — backendDevice, backendId, gpuMemTotalMb, gpuMemFreeMb — through all three stats layers: the addon read shape (addon-responses.ts), the transcribe op mapping, and the public transcribeStatsSchema.
• All four are optional: CPU runs and the parakeet engine simply omit the ones they don't populate; -1 is the no-accounting sentinel for the GPU memory fields.

🧪 How was it tested?

• New unit test transcription-stats-schema.test.ts: round-trips the GPU fields, asserts they're optional (CPU/parakeet path), accepts the -1 sentinel, and rejects non-numeric backend values (4/4 tests, 11/11 asserts).
• bun run typecheck and eslint on changed files pass.
• bare-sdk parity (check:deps-vs-sdk) verified — whispercpp is an excluded plugin addon, no sync needed.

🔌 API Changes

// transcribe(...) now surfaces whisper backend/GPU info in the final stats frame
for await (const ev of sdk.transcribe({ modelId, audioChunk, metadata: true })) {
  if (ev.done && ev.stats) {
    console.log(ev.stats.backendDevice);  // 0 = CPU, 1 = GPU
    console.log(ev.stats.backendId);      // GPU backend family (BackendId enum)
    console.log(ev.stats.gpuMemTotalMb);  // -1 when no memory accounting
    console.log(ev.stats.gpuMemFreeMb);
  }
}

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