refactor: split the aura-std roster into C28 layer crates

Phase 4 of the Stratification milestone. aura-std held four C28 ladder
layers in one roster; this cuts them into layer-aligned, aura-core-only
node crates so the import direction is enforced by the crate graph:

- aura-std        — engine nodes only (arithmetic/logic/rolling + sinks)
- aura-market     — session, resample
- aura-strategy   — bias, stops, sizer, cost-model machinery
- aura-backtest   — sim_broker, position_management
- aura-vocabulary — the relocated closed std_vocabulary roster

Node modules move verbatim (byte-identical renames); consumers are
rewired by import path only. A new structural test
(aura-vocabulary/tests/c28_layering.rs) asserts each node crate's
[dependencies] stay within its C28-permitted inner set, catching the
acyclic-but-outward violation the compiler misses.

Behaviour byte-identical: full workspace suite green (1448 tests), no
golden edited, clippy -D warnings clean. C28 Status block updated.

closes #288

Cargo.lock

@@ -105,6 +105,13 @@ dependencies = [
  "serde_json",
 ]
 
+[[package]]
+name = "aura-backtest"
+version = "0.1.0"
+dependencies = [
+ "aura-core",
+]
+
 [[package]]
 name = "aura-bench"
 version = "0.1.0"
@@ -139,6 +146,7 @@ dependencies = [
 name = "aura-cli"
 version = "0.1.0"
 dependencies = [
+ "aura-backtest",
  "aura-campaign",
  "aura-composites",
  "aura-core",
@@ -147,6 +155,8 @@ dependencies = [
  "aura-registry",
  "aura-research",
  "aura-std",
+ "aura-strategy",
+ "aura-vocabulary",
  "clap",
  "data-server",
  "libc",
@@ -162,9 +172,11 @@ dependencies = [
 name = "aura-composites"
 version = "0.1.0"
 dependencies = [
+ "aura-backtest",
  "aura-core",
  "aura-engine",
  "aura-std",
+ "aura-strategy",
  "serde_json",
 ]
 
@@ -181,8 +193,12 @@ name = "aura-engine"
 version = "0.1.0"
 dependencies = [
  "aura-analysis",
+ "aura-backtest",
  "aura-core",
+ "aura-market",
  "aura-std",
+ "aura-strategy",
+ "aura-vocabulary",
  "chrono",
  "chrono-tz",
  "rayon",
@@ -194,15 +210,27 @@ dependencies = [
 name = "aura-ingest"
 version = "0.1.0"
 dependencies = [
+ "aura-backtest",
  "aura-core",
  "aura-engine",
+ "aura-market",
  "aura-std",
+ "aura-strategy",
  "chrono",
  "chrono-tz",
  "data-server",
  "zip",
 ]
 
+[[package]]
+name = "aura-market"
+version = "0.1.0"
+dependencies = [
+ "aura-core",
+ "chrono",
+ "chrono-tz",
+]
+
 [[package]]
 name = "aura-registry"
 version = "0.1.0"
@@ -211,6 +239,8 @@ dependencies = [
  "aura-engine",
  "aura-research",
  "aura-std",
+ "aura-strategy",
+ "aura-vocabulary",
  "serde",
  "serde_json",
 ]
@@ -229,11 +259,32 @@ dependencies = [
 name = "aura-std"
 version = "0.1.0"
 dependencies = [
+ "aura-backtest",
  "aura-core",
+ "aura-strategy",
  "chrono",
  "chrono-tz",
 ]
 
+[[package]]
+name = "aura-strategy"
+version = "0.1.0"
+dependencies = [
+ "aura-core",
+]
+
+[[package]]
+name = "aura-vocabulary"
+version = "0.1.0"
+dependencies = [
+ "aura-backtest",
+ "aura-core",
+ "aura-market",
+ "aura-std",
+ "aura-strategy",
+ "toml",
+]
+
 [[package]]
 name = "autocfg"
 version = "1.5.1"