test(05-00): update registry.test.ts to use .fields access for TECH-03 shape

- Update BACKEND_REGISTRY[backend].length → .fields.length
- Update iteration to use BACKEND_REGISTRY[backend].fields
- Update field lookups (.find/.map) to go through .fields
- Add new test: each backend has displayName and description metadata (RED)

src/schemas/registry.test.ts

@@ -12,13 +12,13 @@ describe('Backend Schema Registry', () => {
 
   it('each backend has at least one field definition', () => {
     for (const backend of EXPECTED_BACKENDS) {
-      expect(BACKEND_REGISTRY[backend].length).toBeGreaterThan(0);
+      expect(BACKEND_REGISTRY[backend].fields.length).toBeGreaterThan(0);
     }
   });
 
   it('each FieldDef has a non-empty key (snake_case, no camelCase)', () => {
     for (const backend of EXPECTED_BACKENDS) {
-      for (const field of BACKEND_REGISTRY[backend]) {
+      for (const field of BACKEND_REGISTRY[backend].fields) {
         expect(field.key).toBeTruthy();
         // Reject camelCase — rclone keys are snake_case or lowercase
         expect(field.key).not.toMatch(/[A-Z]/);
@@ -28,28 +28,35 @@ describe('Backend Schema Registry', () => {
 
   it('each FieldDef has a non-empty label', () => {
     for (const backend of EXPECTED_BACKENDS) {
-      for (const field of BACKEND_REGISTRY[backend]) {
+      for (const field of BACKEND_REGISTRY[backend].fields) {
         expect(field.label).toBeTruthy();
       }
     }
   });
 
   it('Azure Blob has account field (required)', () => {
-    const accountField = BACKEND_REGISTRY.azureblob.find(f => f.key === 'account');
+    const accountField = BACKEND_REGISTRY.azureblob.fields.find(f => f.key === 'account');
     expect(accountField).toBeDefined();
     expect(accountField!.required).toBe(true);
   });
 
   it('S3 has access_key_id, secret_access_key, and region fields', () => {
-    const keys = BACKEND_REGISTRY.s3.map(f => f.key);
+    const keys = BACKEND_REGISTRY.s3.fields.map(f => f.key);
     expect(keys).toContain('access_key_id');
     expect(keys).toContain('secret_access_key');
     expect(keys).toContain('region');
   });
 
   it('S3-compatible has endpoint field (required)', () => {
-    const endpointField = BACKEND_REGISTRY['s3-compatible'].find(f => f.key === 'endpoint');
+    const endpointField = BACKEND_REGISTRY['s3-compatible'].fields.find(f => f.key === 'endpoint');
     expect(endpointField).toBeDefined();
     expect(endpointField!.required).toBe(true);
   });
+
+  it('each backend entry has displayName and description metadata', () => {
+    for (const backend of EXPECTED_BACKENDS) {
+      expect(BACKEND_REGISTRY[backend].displayName).toBeTruthy();
+      expect(BACKEND_REGISTRY[backend].description).toBeTruthy();
+    }
+  });
 });