ax-core — the anomalyx contract

This crate is the executable contract the article argues for: the typed record model every input collapses into, the anomaly taxonomy, the deterministic reductions detectors are built on, and the tq1 output envelope. It deliberately depends on nothing heavy (no Polars, no math crates) so the contract stays engine-independent and the mutation-test gate stays fast.

Design commitments, straight from the article:

• Determinism is UX: see [det] — every reduction is order-independent.
• Honest absence: [value::Value::Null] never becomes a 0.0; detectors that can't run are recorded in [envelope::Absence].
• Handle-based evidence: compact [finding::Finding]s carry stable [finding::Handle]s that explain resolves on demand.
• Versioned protocol: [envelope::PROTOCOL] and committed [envelope::ExitCode]s.