Implement CENG-WP-0002: package distribution and publish readiness

Resolve ADR-0002 in umbrella, add install docs, contract sync runbook,
publishing checklist, and package files whitelist.

wiki/README.md

@@ -0,0 +1,22 @@
+# Wiki — citation-engine
+
+## SharedContracts sync
+
+`SharedContracts.md` in this directory is a **conformance copy** for tests
+(e.g. `evidence-link.test.ts` enum parity checks). It is not authoritative.
+
+**Authoritative source:** `citation-evidence/wiki/SharedContracts.md`
+
+### When contracts change
+
+1. Land the change in `citation-evidence/wiki/SharedContracts.md` (and any
+   runtime types in `citation-engine/src/shared/` if enums or shapes change).
+2. Copy/sync to `citation-engine/wiki/SharedContracts.md`.
+3. Run `pnpm test` in **both** repos.
+4. Bump `@citation-evidence/engine` version if the change is breaking for
+   consumers.
+
+### Test reference path
+
+`src/shared/evidence-link.test.ts` reads `wiki/SharedContracts.md` relative
+to `src/shared/` (`../../wiki/SharedContracts.md`).