fix(frontend): enforce no-explicit-any and fix test stability

- Change ESLint no-explicit-any from 'warn' to 'error'
- Replace 'any' with 'unknown as string' in initials.pipe.spec
- Fix StudentService tests to handle Apollo watchQuery multiple emissions
- Add filter for loading state before asserting in tests

Stricter type checking improves code quality.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/frontend/eslint.config.mjs

@@ -25,7 +25,7 @@ export default [
       ...tseslint.configs.recommended.rules,
       "@typescript-eslint/no-unused-vars": ["error", { argsIgnorePattern: "^_" }],
       "@typescript-eslint/explicit-function-return-type": "off",
-      "@typescript-eslint/no-explicit-any": "warn",
+      "@typescript-eslint/no-explicit-any": "error",
       "@angular-eslint/directive-selector": ["error", { type: "attribute", prefix: "app", style: "camelCase" }],
       "@angular-eslint/component-selector": ["error", { type: "element", prefix: "app", style: "kebab-case" }],
     },

src/frontend/src/app/core/services/student.service.spec.ts

@@ -1,5 +1,6 @@
 import { TestBed } from '@angular/core/testing';
 import { ApolloTestingController, ApolloTestingModule } from 'apollo-angular/testing';
+import { filter, take } from 'rxjs';
 import { StudentService } from './student.service';
 import { GET_STUDENTS, GET_STUDENT } from '@core/graphql/queries/students.queries';
 import { CREATE_STUDENT, DELETE_STUDENT } from '@core/graphql/mutations/students.mutations';
@@ -29,7 +30,11 @@ describe('StudentService', () => {
         { id: 2, name: 'María García', email: 'maria@test.com', totalCredits: 3, enrollments: [] },
       ];
 
-      service.getStudents().subscribe((result) => {
+      // Filter for the response with data (loading = false)
+      service.getStudents().pipe(
+        filter(result => !result.loading && result.data.length > 0),
+        take(1)
+      ).subscribe((result) => {
         expect(result.data).toEqual(mockStudents);
         done();
       });
@@ -40,7 +45,10 @@ describe('StudentService', () => {
     });
 
     it('should return empty array when no students', (done) => {
-      service.getStudents().subscribe((result) => {
+      service.getStudents().pipe(
+        filter(result => !result.loading),
+        take(1)
+      ).subscribe((result) => {
         expect(result.data).toEqual([]);
         done();
       });
@@ -57,7 +65,10 @@ describe('StudentService', () => {
         totalCredits: 6, enrollments: []
       };
 
-      service.getStudent(1).subscribe((result) => {
+      service.getStudent(1).pipe(
+        filter(result => !result.loading && result.data !== null),
+        take(1)
+      ).subscribe((result) => {
         expect(result.data).toEqual(mockStudent);
         done();
       });
@@ -68,7 +79,10 @@ describe('StudentService', () => {
     });
 
     it('should return null when student not found', (done) => {
-      service.getStudent(999).subscribe((result) => {
+      service.getStudent(999).pipe(
+        filter(result => !result.loading),
+        take(1)
+      ).subscribe((result) => {
         expect(result.data).toBeNull();
         done();
       });

src/frontend/src/app/shared/pipes/initials.pipe.spec.ts

@@ -28,8 +28,9 @@ describe('InitialsPipe', () => {
   });
 
   it('should handle null-like values', () => {
-    expect(pipe.transform(null as any)).toBe('');
-    expect(pipe.transform(undefined as any)).toBe('');
+    // Test runtime safety for edge cases (null/undefined passed from templates)
+    expect(pipe.transform(null as unknown as string)).toBe('');
+    expect(pipe.transform(undefined as unknown as string)).toBe('');
   });
 
   it('should uppercase initials', () => {