Standardize compute job concurrency configuration by introducing a shared
COMPUTE_JOB_CONCURRENCY setting, replacing separate PDF and Whisper concurrency
controls. Add cross-platform CPU core detection and thread budgeting utilities,
and update both ONNX model execution and concurrency limiters to use dynamic
thread allocation per job. Refactor environment variable docs and examples to
reflect unified concurrency management. Streamline PDF.js font path resolution
for improved reliability across environments.
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