Add automated playwright tests

[edmcman]

No description provided.

[Copilot]

Pull request overview

This PR adds automated end-to-end testing infrastructure using Playwright to test the Link Hints browser extension. The tests walk through the interactive tutorial, verifying that the extension's hint system works correctly across different modes and interactions.

Key Changes

• Adds Playwright test framework with Firefox browser support
• Implements comprehensive tutorial walkthrough test with snapshot testing
• Modifies shadow DOM mode to be "open" in development for test accessibility
• Adds CI workflow to run tests automatically on pull requests
• Includes devcontainer configuration for consistent development environment

Reviewed changes

Copilot reviewed 18 out of 29 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/tutorial.spec.ts	Main test file implementing tutorial walkthrough with helper functions for hint activation and snapshotting
playwright.config.ts	Configures Playwright with Firefox in headed mode (required for extensions) with 60s timeout
package.json	Adds Playwright dependencies and test:playwright script
src/renderer/Program.ts	Changes shadow DOM mode from "closed" to "open" in dev mode for test accessibility
project.config.ts	Modifies compiled output path to "compiled-dev" when not building for production
.github/workflows/ci.yml	Adds test job with xvfb for headless browser testing in CI
.devcontainer/devcontainer.json	Configures dev container with Node 18, xvfb, and Playwright dependencies
.github/copilot-instructions.md	Documents project structure and conventions for AI assistants
.gitignore & .prettierignore	Excludes test results and snapshot directories
tests/-snapshots/.html	Snapshot files for visual regression testing of hint rendering
tests/-snapshots/.png	Screenshot snapshots for visual comparison

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[Copilot]

The comment says "Press 'o'" but the code presses 'e'. This inconsistency between the comment and the implementation suggests either the comment is wrong or the wrong key is being pressed.

Suggested change

	await page.keyboard.press("e");
	await page.keyboard.press("o");

[Copilot]

This hardcoded wait timeout is a test anti-pattern that can cause flakiness. The comment indicates the author wants to remove it. Consider replacing with a proper wait condition that checks for the actual state change you're waiting for, or use Playwright's auto-waiting features.

Suggested change

await page.waitForTimeout(200);