Bind BFV proofs to exact supported parameter presets #1674

Audit reference: I30

What can go wrong

Unsupported BFV parameter combinations could select the wrong proof preset, and an invalid polynomial degree could panic during construction.

When it happens

This boundary is reached when clients build verifiable encryption inputs and when proof code resolves the requested BFV parameters.

What changed

Only exact supported parameter pairs resolve to a preset, and canonical parameter construction is fallible.

Why the change works

The encryption parameters and the circuit constants must now come from the same known tuple; malformed inputs return an error instead of diverging or panicking.

Checks

Noncanonical tuple, invalid degree, supported preset, and variance tests pass.