feat(core-eslint): add entity-must-have-test and no-relative-parent-import rules

Two CLAUDE.md conventions had no mechanical gate, so both drifted:
entity models shipped without sibling tests, and feature test files
imported src modules via `../` instead of the `@/` alias.

- `entity-must-have-test` — every entities/models/<x>.ts needs a sibling
  <x>.test.ts (errors and barrels excluded).
- `no-relative-parent-import-in-tests` — feature test files must import
  src via `@/`, not `../`. Scoped to feature packages; core packages are
  governed by their own generator templates.

Both register at warn level, bringing the conformance rule count to 15.

packages/core-eslint/base.js

@@ -55,6 +55,8 @@ export default [
       "conformance/pii-declaration-must-be-complete": "warn",
       "conformance/no-undeclared-consent-check": ["warn", { repoRoot }],
       "conformance/no-undeclared-rate-limit": ["warn", { repoRoot }],
+      "conformance/entity-must-have-test": "warn",
+      "conformance/no-relative-parent-import-in-tests": "warn",
     },
   },
   {