Add LICENSE, versioned evidence schema, pluggable normalizer, property tests

- Apache-2.0 LICENSE file (enterprise blocker fixed)
- Evidence pack JSON Schema (src/evidence_schema.json) with EVIDENCE_SCHEMA_VERSION
  constant embedded in every pack. Consumers MUST check schema_version before parsing.
- `usageguard describe` CLI command dumps the schema specification
- Normalizer trait (dyn Normalizer) replaces hardcoded alias map:
  - BuiltinNormalizer: default 90+ aliases (Stripe, Orb, LangChain, CSV)
  - Pipeline::with_normalizer(Box<dyn Normalizer>) for custom sources
  - No recompile needed to add new event formats
- Property tests (proptest): seal/verify round-trip, tamper detection,
  wrong-key detection across random batches of 1-20 events
- Custom normalizer integration test (end-to-end with Pipeline)
- Evidence schema validation test

61 tests green. Zero warnings.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Doug Hamaker

Cargo.lock

@@ -3,7 +3,7 @@ name = "usageguard"
 version = "0.1.0"
 edition = "2021"
 description = "Deterministic usage-event validation engine for billing pipelines"
-license = "MIT"
+license = "Apache-2.0"
 
 [dependencies]
 chrono = { version = "0.4", features = ["serde"] }
@@ -16,6 +16,9 @@ serde_json = "1"
 sha2 = "0.10"
 uuid = { version = "1", features = ["v4"] }
 
+[dev-dependencies]
+proptest = "1"
+
 [[bin]]
 name = "usageguard"
 path = "src/main.rs"