audit: cycle 0030 (#35) — drift-clean; named param binding

cycle 0030 tidy (clean). The architect drift review against docs/design/INDEX.md
and CLAUDE.md found the cycle drift-clean: every load-bearing contract the named
binding layer touches holds.

- C1 / C12 / C19 / C23: a pure authoring layer — sweep.rs, the lowering path,
  collect_params, and param_space() are unchanged; with/axis/Binder/SweepBinder/
  resolve/resolve_axes all terminate into the existing bootstrap_with_params /
  GridSpace::new / sweep. No new state, no concurrency, no path into the run loop.
  Equivalence pinned by named_binder_runs_bit_identical_to_positional and
  named_axes_grid_parity_with_positional. The match key is the exact param_space()
  name (p.name == name), read-only.
- C7: pure-equality kind check (v.kind() != p.kind), no coercion.
- C16 / C10: std-only (the e97906a pin added a test, not a dependency); builder
  idiom (.with()/.axis()), no DSL/macro.
- The full BindError enum (incl. EmptyAxis) is constructed (EmptyAxis in
  resolve_axes) — no dead variant. No .bind() ships — the #55 structural-constant
  reservation is intact. The resolve/resolve_axes two-phase duplication is the
  documented accepted debt (spec §Components), not silent drift.

Resolution: one Nit fixed inline — a redundant `use crate::GridSpace;` in the
blueprint.rs test module (GridSpace is already in scope via `use super::*`).
Removed; the parity test still compiles, full `cargo test --workspace` green and
`cargo clippy --workspace --all-targets -- -D warnings` clean.

Regression gate: none configured (profile regression: []); architect is the gate.

This closes the named-binding feature (single run + sweep). Note: this is a
cycle drift-clean close, not a milestone close — the milestone fieldtest for
"The World — parameter-space & sweep" remains a deliberate manual act.

closes #35

crates/aura-engine/src/blueprint.rs

@@ -917,7 +917,6 @@ fn slot_kind(t: Target, flat_signatures: &[NodeSchema]) -> Result<ScalarKind, Co
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::GridSpace;
     use aura_core::{Ctx, FieldSpec, Firing, NodeSchema, Timestamp};
     use aura_std::{Ema, Exposure, Recorder, SimBroker, Sma, Sub};
     use std::sync::mpsc;