harden report contract projection identity

Add a runtime report schema v1 contract so downstream consumers can negotiate structured fields, verify canonical report identity, and audit projection redactions without reverse-engineering prose.\n\nConstraint: Task 2 scope was limited to report schema/projection/redaction modules/docs/tests and prohibited .omx/ultragoal mutation.\nRejected: Wiring into broader CLI report emitters | kept this slice focused on the reusable contract and deterministic fixtures.\nConfidence: high\nScope-risk: narrow\nDirective: Future report emitters should build canonical payloads through CanonicalReportV1 before projecting audience-specific views.\nTested: cargo test -p runtime report_schema -- --nocapture; cargo test -p runtime lane_events -- --nocapture; cargo check -p runtime\nNot-tested: cargo clippy -p runtime --all-targets -- -D warnings remains blocked by pre-existing non-task warnings in compact.rs, file_ops.rs, policy_engine.rs, sandbox.rs.

rust/crates/runtime/tests/fixtures/report_schema_v1/README.md

@@ -0,0 +1,11 @@
+# Report schema v1 fixture set
+
+Validated by `cargo test -p runtime report_schema -- --nocapture`.
+
+The in-code fixture in `runtime::report_schema::tests::fixture_report` covers:
+- fact / hypothesis / confidence labels
+- negative evidence with checked surfaces and query window
+- field-level delta attribution
+- canonical report id plus content hash
+- deterministic projection/redaction provenance
+- consumer capability negotiation and downgraded projections