feat: measurement's first deflatable metric — the Information Coefficient

Give a measurement run a standalone post-run quality score: the Information
Coefficient (IC), corr(signal_t, forward_return_{t+h}), with a permutation
null model. Before this a measurement run persisted only tap names and series
(MeasurementReport) — inspectable but not rankable or deflatable. IC is the
first metric measurement supplies: the tap-to-scalar reduction the C28
process-column / metric-interface seam anticipates ("a named metric vocabulary
supplied by measurement and backtest instead of baked in R-only").

Surface: `aura measure ic <run> --signal <tap> --price <tap> [--horizon]
[--permutations] [--seed]`. It reads the run's two recorded tap traces, builds
the forward-return series offline over the recorded price spine, aligns
signal -> return by exact timestamp, computes the IC, and prints it with a
one-sided permutation-null overfit probability (Laplace-smoothed, mirroring the
R deflation arm's formula in optimize_deflated).

Placement follows the C28 ladder: the generic pieces — pearson_corr and a
Fisher-Yates permute over SplitMix64 — land in aura-analysis (the domain-free
statistics foundation, beside resample_block); the IC semantics (forward-return
horizon, the offline join) and the CLI verb land in aura-cli (the shell). The
run path (run_measurement), MeasurementReport, the trace store, and the registry
metric vocabulary are untouched — existing `aura run` output stays byte-identical
(the C18 golden run_prints_json_and_exits_zero stays green).

Causality (C2): the forward-return read close_{t+h} is over a completed run's
recorded trace, not an in-graph node. A look-ahead signal is structurally
impossible in a causal run, so the engineered-vs-noise acceptance property is
unit-tested over hand-built offline series (perfect signal -> IC ~= 1, p < 0.05;
a varying but exactly-uncorrelated signal -> IC = 0, not significant;
constant/degenerate -> the (0.0, 1.0) floor), while the E2E validates the CLI
wiring, report well-formedness, determinism, and the error paths over a real run.

This lands the second, structurally distinct null-model computation (permutation,
beside the moving-block bootstrap behind R). That makes the deferred registry
deflation-vocabulary abstraction (#147 item 2) demand-driven rather than
speculative — the next cycle.

Verified: cargo test --workspace green (incl. the new aura-analysis unit tests,
the aura-cli ic_* unit tests, and the measure_ic E2E); cargo clippy --workspace
--all-targets -D warnings clean; the C18 byte-identity golden unchanged.

closes #290
refs #147

crates/aura-cli/Cargo.toml

@@ -24,6 +24,7 @@ aura-campaign = { path = "../aura-campaign" }
 aura-std = { path = "../aura-std" }
 aura-strategy = { path = "../aura-strategy" }
 aura-backtest = { path = "../aura-backtest" }
+aura-analysis = { path = "../aura-analysis" }
 aura-vocabulary = { path = "../aura-vocabulary" }
 aura-ingest = { path = "../aura-ingest" }
 # data-server: the local M1 archive `aura run --real` streams from. Mirrors the