feat(tests): add complete test suite with unit, integration, E2E and mutation testing

- Add Vitest unit tests: getPattern (70), presets with Zod oracle (21), helpers (11)
- Add Vitest integration tests: banner.js (27), localStorage (16)
- Add Playwright E2E tests: banner customization, accessibility (axe-core WCAG 2.1 AA), performance
- Add Stryker mutation testing config for presets.js and helpers.js
- Add ESLint + eslint-plugin-security for static analysis (OWASP Top 10)
- Add @faker-js/faker for test data generation
- Add Zod schemas as validation oracles (PresetSchema, ThemeSchema, PatternResultSchema)
- Add vitest.config.js with jsdom environment and coverage thresholds (lines>=70%, functions>=80%)
- Add playwright.config.ts with 4 browsers (chromium, firefox, webkit, mobile-chrome)
- Add TESTING.md with full technical documentation of the test suite
- Add trabajo.md with project presentation and analysis
- Update package.json: add type:module + all testing devDependencies + npm scripts

Coverage achieved: 74% lines, 72% branches, 100% functions
Bugs found: 7 (including 1 critical TypeError in banner.js)
E2E results: 29/34 pass, 5 fail (real production bugs - accessibility violations WCAG 2.1)

Author: Edithct

TESTING.md

@@ -0,0 +1,20 @@
+import js from "@eslint/js";
+import security from "eslint-plugin-security";
+
+export default [
+  js.configs.recommended,
+  {
+    plugins: { security },
+    rules: {
+      ...security.configs.recommended.rules,
+      "no-eval": "error",
+      "no-implied-eval": "error",
+      "no-new-func": "error",
+      "no-script-url": "error",
+      "no-unused-vars": "warn",
+      "no-console": "off",
+    },
+    files: ["js/**/*.js"],
+    ignores: ["js/data/patterns.js"],
+  },
+];