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/rules/no-relative-parent-import-in-tests.js

@@ -0,0 +1,49 @@
+/**
+ * Feature test files import from `src/` through the `@/` alias, never via
+ * `../` parent traversal (CLAUDE.md "Key Conventions"). A `../` import in a
+ * test file is always reaching across `src/` directories — `@/` keeps those
+ * imports stable under file moves and makes the test's dependencies legible.
+ *
+ * Scoped to feature packages (`packages/<name>/src/`, excluding `core-*`):
+ * the convention is part of the feature template's contract. Core packages
+ * are generated and governed by their own templates, and tooling packages
+ * (turbo/generators, scripts) legitimately use relative paths.
+ */
+function isFeatureSrcTestFile(filename) {
+  const normalized = filename.replace(/\\/g, "/");
+  if (!normalized.endsWith(".test.ts") && !normalized.endsWith(".test.tsx")) {
+    return false;
+  }
+  return /\/packages\/(?!core-)[^/]+\/src\//.test(normalized);
+}
+
+/** @type {import("eslint").Rule.RuleModule} */
+export default {
+  meta: {
+    type: "problem",
+    docs: {
+      description:
+        "Feature test files must import src modules via the @/ alias, not ../ parent paths.",
+    },
+    schema: [],
+    messages: {
+      relativeParentImport:
+        'Test file imports "{{source}}" with a ../ parent path. Use the "@/" alias for src imports (e.g. "@/application/...").',
+    },
+  },
+  create(context) {
+    if (!isFeatureSrcTestFile(context.filename)) return {};
+    return {
+      ImportDeclaration(node) {
+        const source = node.source.value;
+        if (typeof source === "string" && source.startsWith("../")) {
+          context.report({
+            node: node.source,
+            messageId: "relativeParentImport",
+            data: { source },
+          });
+        }
+      },
+    };
+  },
+};