test(issue-5): implement fail-closed evidence dispatch and fix VALID_STATUSES citation

- Fix Codex [P1]: add SUPPORTED_SOURCE_KINDS dispatch and enforce fail-closed rejection for non-herdr observed items without independent schema
- Add strict correspondence checks for native Herdr observed items (agent_status, native schema, session UUID)
- Add negative test reproducing Codex in-memory mutation of finalized_candidate
- Fix Claude Finding 2: update VALID_STATUSES citation in baseline.md to registry.py:38
- Update Phase 0 collected test counts to 499 in contract docs

docs/contracts/issue-5/task.md

@@ -9,7 +9,7 @@
 ## Phase 0: 사전 계약 기준선 및 Fixture 수집 (이번 실행 범위)
 
 - [x] **P0-01** 기준 commit, dirty diff, Herdr/Python 버전, pytest collection 수 기록.
-  - *증거*: Commit `47640e2`, Herdr `0.8.2`, Python `3.9.6`, Pytest `469 tests collected initially` ➔ `484 tests collected with Phase 0 suite` (+15 contract & mutation tests).
+  - *증거*: Commit `47640e2`, Herdr `0.8.2`, Python `3.9.6`, Pytest `469 tests collected initially` ➔ `499 tests collected with Phase 0 suite` (+30 contract & mutation tests).
 - [x] **P0-02** `docs/contracts/issue-5/baseline.md` 작성: 공개 CLI/default/invalid input/stdout-stderr/exit/interpreter/path/signal 계약과 소스·기존 테스트 매핑.
   - *증거*: `docs/contracts/issue-5/baseline.md` §2 (`--all-reviewer` 우선순위 및 L192–196 소스 매핑 반영).
 - [x] **P0-03** event schema/HMAC/seq/retain/audit/디스크 fallback 및 publisher 실패 후 로컬 commit 동작 기록.