Consume the shared complex arithmetic field contract

[isomorphisms]

Purpose

Make the live whole-plane explorer an explicit application consumer of the canonical complex/projective corpus without moving app machinery into the compiler or reintroducing migrated Lacunary/lasso work.

Existing live model preserved

The native walk already represents q as complex polynomial coefficients and evolves it with complex multiplication. The fragment already evaluates

f(z) = R(z) exp(q(z))

by adding Re(q) to log modulus and Im(q) to phase after the explicit zero/pole divisor. This PR anchors that existing implementation to the shared cross-backend contract rather than replacing it.

Consumer acceptance

The unit-test workflow now checks out the exact canonical math/complex-projective-semantics branch. The application fixture consumes the shared field model and the shared explicit zero/pole divisor.

The application retains its own live u=z/6 coefficient normalization/budget, so it does not force its random-walk policy into the compiler or x86 backend and does not require pixel equality with the x86 headless renderer.

Tests verify:

• the application fixture is inside the live coefficient budget;
• sampled exp(q) values are finite and nonzero;
• holomorphic_q contains polynomial complex arithmetic but no phase/log/magnitude/conjugation/derivative observation;
• the walk's direction_at remains polynomial complex arithmetic;
• the shared field/divisor contract matches the application consumer fixture.

A provenance receipt is uploaded with both the application head and canonical semantic target SHA.

Projective boundary

The finite interactive viewport does not currently require a runtime CP^1 point at infinity. This PR does not invent one just to advertise projective integration; that stage is recorded SKIP until an actual meromorphic API/serialization operation requires it.

No lasso, overlapping-disc, path, Riemann-surface, or lacunary machinery is reintroduced.