docs: for_spectre_users.md claims Jacobians use JAX autodiff but production uses OpenVAF analytical Jacobians

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File: docs/for_spectre_users.md, line 113

Under 'Key Differences from Spectre', item #3 states:

JAX backend — Jacobians are computed via automatic differentiation rather than hand-coded derivatives. This means any Verilog-A model works without modification.

This is incorrect. Production Jacobians are computed analytically by OpenVAF at compile time, not via JAX autodiff (jax.grad/jacfwd). The same error is noted for index.md and architecture_overview.md in issue #128, but for_spectre_users.md was not included in that issue.