CI: Unit and integration tests

[WezSieTato]

No description provided.

[Copilot]

Pull request overview

This PR introduces an initial automated test setup (unit + E2E/integration) for the Pola browser extension, and refactors EAN validation into a shared module so it can be reused by both the content script and tests.

Changes:

• Added Jest unit tests for EAN validation and popup rendering/behavior (with a Chrome API mock).
• Added Playwright E2E tests that inject the extension’s scripts into real store pages to verify EAN detection.
• Refactored validateEAN into lib/validateEAN.js and updated the popup to inject it before the content script; added GitHub Actions workflows to run tests.

Reviewed changes

Copilot reviewed 12 out of 15 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
test/validateEAN.test.js	New unit tests for EAN-8/EAN-13 validation behavior.
test/popup.test.js	New jsdom-based unit tests for popup UI logic and API/cache handling.
test/mocks/chrome.js	Chrome API mock used by popup unit tests.
test-e2e/ean-detection.spec.js	New Playwright spec that validates EAN detection on real product pages.
README.rst	Documents supported stores / planned support list.
popup/pola.js	Injects lib/validateEAN.js before the content script; exports Pola in test environments.
playwright.config.js	Playwright configuration targeting test-e2e/.
package.json	Adds Node tooling + scripts for unit and integration tests.
package-lock.json	Locks Jest/Playwright dependency tree for CI reproducibility.
lib/validateEAN.js	New shared EAN validation implementation (used by tests and injected into pages).
jest.config.js	Jest configuration (jsdom environment, test match).
content_scripts/pola.js	Removes duplicated inline validateEAN implementation (now relies on injected shared one).
.gitignore	Ignores node_modules/ and Playwright/Jest output (test-results).
.github/workflows/unit_tests.yml	CI job to run Jest unit tests on pushes/PRs.
.github/workflows/integration_tests.yml	CI job to run Playwright integration tests on pushes/PRs + schedule.

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