Sequence ledger, decomposition detection, and cross-agent taint

[arkavo-com]

Spec scenarios: SEQ-007, SEQ-008, SEQ-009

Gap: FederatedItem has no taint classification field. FederatedQuery can filter by agent/session but not by data flow patterns. evaluate_entitlements() checks ABAC but ignores data sensitivity.

RED tests: crates/arkavo-memory/tests/sequence_integrity_test.rs

• federated_item_has_no_taint_classification_field — FAILS
• federated_query_has_no_data_flow_filter — documents gap

Required changes (in crates/arkavo-memory/src/):

• Add taint_classification to FederatedItem
• Add data flow pattern queries to FederatedQuery
• Add taint-aware entitlement evaluation
• Add cross-session decomposition detection

Refs: specs/arkavo-edge/sequence-integrity.spec.yaml