feat: eval package scaffold with CLI, schemas, types, task loader

New package @united-workforce/eval (uwf-eval CLI):

- CLI skeleton: run/report/diff/list subcommands (stubs)
- 5 OCAS schemas: eval-run, judge-frontmatter, judge-upstream,
  judge-hallucination, judge-token-stats
- TaskManifest type + parser/validator for task.yaml
- JudgeOutput/JudgeInput types for judge contract
- EvalRunPayload/EvalRunConfig/EvalJudgeRecord storage types
- 19 unit tests: task loader validation + schema definitions

Refs #69

tsconfig.json

@@ -25,6 +25,7 @@
     { "path": "packages/agent-builtin" },
     { "path": "packages/agent-mock" },
     { "path": "packages/agent-claude-code" },
-    { "path": "packages/cli" }
+    { "path": "packages/cli" },
+    { "path": "packages/eval" }
   ]
 }