feat: add step definitions module and integrate with sidepanel

- Introduced a new module for step definitions in `data/step-definitions.js` to manage shared step metadata.
- Updated `sidepanel.html` to dynamically render steps based on the new step definitions module.
- Refactored `sidepanel.js` to utilize the step definitions for rendering and managing step statuses.
- Enhanced tests to validate the step definitions module and its integration with the sidepanel.
- Cleaned up existing tests to ensure they align with the new structure and functionality.

tests/step-definitions-module.test.js

@@ -0,0 +1,42 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+
+test('step definitions module exposes ordered shared step metadata', () => {
+  const source = fs.readFileSync('data/step-definitions.js', 'utf8');
+  const globalScope = {};
+
+  const api = new Function('self', `${source}; return self.MultiPageStepDefinitions;`)(globalScope);
+  const steps = api.getSteps();
+
+  assert.equal(Array.isArray(steps), true);
+  assert.equal(steps.length >= 9, true);
+  assert.deepStrictEqual(
+    steps.map((step) => step.order),
+    steps.map((step) => step.order).slice().sort((left, right) => left - right)
+  );
+  assert.deepStrictEqual(
+    steps.map((step) => step.key),
+    [
+      'open-chatgpt',
+      'submit-signup-email',
+      'fill-password',
+      'fetch-signup-code',
+      'fill-profile',
+      'oauth-login',
+      'fetch-login-code',
+      'confirm-oauth',
+      'platform-verify',
+    ]
+  );
+});
+
+test('sidepanel html loads shared step definitions before sidepanel bootstrap', () => {
+  const html = fs.readFileSync('sidepanel/sidepanel.html', 'utf8');
+  const definitionsIndex = html.indexOf('<script src="../data/step-definitions.js"></script>');
+  const sidepanelIndex = html.indexOf('<script src="sidepanel.js"></script>');
+
+  assert.notEqual(definitionsIndex, -1);
+  assert.notEqual(sidepanelIndex, -1);
+  assert.ok(definitionsIndex < sidepanelIndex);
+});