feat(hpc): PhiSpiral256 golden-spiral location codebook (anchor layer)

Implements the anchor layer of the PhiSpiral256 leaf-location codec per
.claude/plans/PhiSpiral256-LeafPlanetarium-integration-plan.md — the
orthogonal-location lane that recovers what PolarQuant (magnitude) discards.

  - SpiralChart::{Euclidean, Poincare{rho_max}} — equal-Euclidean-area
    (r=sqrt(u)) vs equal-hyperbolic-area (r=tanh(rho/2), arcosh-spaced).
  - PhiSpiralCenterQ15 — Q15 i16/i16/u16 fixed-point centers (the precise
    location tier; 256-anchor table is 1536 B).
  - PhiSpiral256::{new, center_xy, nearest, distance, k_nearest} — golden
    angle theta = 2*pi*frac(k/phi), nearest-anchor scalar scan, on-demand
    distance/neighbor (no stored 128 KB table).
  - PhiSpiralLeafAtom16 — packed (spiral_id, mag4, BGZ17 offset/stride
    family indices). BGZ17 = Base17, offset family in ~17..27, stride {2,4};
    families are indices, not values.

Grounding established this session by reading the real code:
  - golden-angle primitive already ships (surround_metadata::GOLDEN_ANGLE,
    holo Fibonacci carriers) — reused the constant, new sibling module.
  - pseudo-Poincare is free only near the origin (tanh(x)~x); the charts
    diverge toward the boundary where only a true Poincare chart preserves
    Mobius-equivariance. Documented as a regime, with tests for both.
  - precision ladder: Base17 (coarse) -> PhiSpiral256 (byte) -> i16/i16 (full).

Module doc records the design trajectory (phase-centric, not offset/stride;
a Gaussian splat = anchor + 2D covariance reusing splat3d Spd/conic, not a
bare point; hemispheric Poincare placement; optional spatial magnitude).
This commit is the first, smallest, testable layer. 12 tests, all green.

https://claude.ai/code/session_01HbqooFZHAjaUtFEzhA1R2u

Author: claude

src/hpc/mod.rs

@@ -37,6 +37,9 @@ pub mod lapack;
 pub mod fft;
 pub mod vml;
 pub mod packed;
+// PhiSpiral256 — golden-spiral leaf-location codec (orthogonal location lane,
+// sibling to CAM_PQ meaning / PolarQuant magnitude).
+pub mod phi_spiral;
 
 // Cognitive layer types (migrated from rustynum-core)
 #[allow(missing_docs)]