test(speckl): lock in enum interface classification (cycle 60)

Adds a regression test that confirms a bare-identifier interface (no
methods with parens, no fields with colons) parses as kind: 'enum'
with the variants on its methods[] array. The .proto generator already
emits these correctly as 'enum X { X_UNSPECIFIED = 0; FOO = 1; ... }'
- confirmed end-to-end by running generateProtobuf against the
federated-meetup CustodyTier shape.

This was a verification cycle rather than a feature cycle: the compiler
already does the right thing for enums, but without a regression test
a future refactor of classifyInterfaces or parseInterface could break
this silently. The test pins the behavior so a PR that breaks enum
emission will fail CI.

All 49 tests pass (48 + 1 new). tsc build clean.

Reference: federated-meetup.speckdl CustodyTier shape
  interface CustodyTier {
    ColdHardware
    HotSigning
    ThresholdSplit
    BackupOnly
    Compromised
  }

compiler/__tests__/parser.test.ts

@@ -742,4 +742,28 @@ speck Second {
       }
     });
   });
+
+  // Cycle 60: enum interfaces (e.g. CustodyTier) parse as `kind: 'enum'`
+  // and the .proto generator emits a real `enum X { ... }` block.
+  describe('enum interfaces (cycle 60)', () => {
+    it('should classify bare-identifier interfaces as enums', () => {
+      const content = `speck FederatedMeetup {
+  interface CustodyTier {
+    ColdHardware
+    HotSigning
+    ThresholdSplit
+    BackupOnly
+    Compromised
+  }
+}`;
+      const ast = parseSpeckContent(content);
+      const tier = ast.specks[0].members.find(m => m.name === 'CustodyTier');
+      if (tier?.type === 'interface') {
+        expect(tier.kind).toBe('enum');
+        expect(tier.methods.map(m => m.name)).toEqual([
+          'ColdHardware', 'HotSigning', 'ThresholdSplit', 'BackupOnly', 'Compromised'
+        ]);
+      }
+    });
+  });
 });