test(e2e): load secret from env

[duyhungtnn]

This pull request updates how environment variables are managed for E2E (end-to-end) tests by switching from hardcoded configuration in the test config file to using a .env file and the dotenv package. It also updates the documentation to reflect these changes and makes some minor adjustments to dependencies in package.json.

fix #193

[Copilot]

Pull request overview

This PR updates the E2E test setup to load required secrets from environment variables (optionally via a .env file) instead of hardcoding them in the AVA config, addressing issue #193.

Changes:

• Load .env via dotenv and wire E2E config values from process.env.
• Update README E2E instructions and add .env.example template.
• Add dotenv to devDependencies and ignore local .env files.

Reviewed changes

Copilot reviewed 4 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
ava-e2e.config.mjs	Loads .env and passes env-derived secrets into AVA’s environmentVariables for E2E runs.
package.json	Adds dotenv (dev dependency) and reorders some dependencies.
README.md	Documents required env vars / .env usage for E2E testing.
.env.example	Provides a template for required E2E environment variables.
.gitignore	Prevents committing local .env secrets.
yarn.lock	Locks dotenv dependency.

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[duyhungtnn]

Hi @cre8ivejp, please help me to take a look.
These changes were made because adding secrets to ava-e2e.config.mjs can easily lead to accidentally committing them and leaking secrets.