docs: add signal forms playground template

(cherry picked from commit e0eb619c03)

adev/src/content/tutorials/playground/4-signal-forms/config.json

@@ -0,0 +1,5 @@
+{
+  "type": "editor-only",
+  "title": "Signals forms template",
+  "openFiles": ["src/main.ts", "src/main.css"]
+}

adev/src/content/tutorials/playground/4-signal-forms/src/main.css

@@ -0,0 +1,70 @@
+form {
+  display: flex;
+  flex-direction: column;
+  gap: 1rem;
+  max-width: 400px;
+  padding: 1rem;
+  font-family:
+    Inter,
+    system-ui,
+    -apple-system,
+    sans-serif;
+}
+
+div {
+  display: flex;
+  flex-direction: column;
+  gap: 0.25rem;
+}
+
+label {
+  display: flex;
+  flex-direction: column;
+  gap: 0.25rem;
+  font-weight: 500;
+}
+
+input {
+  padding: 0.5rem;
+  border: 1px solid #ccc;
+  border-radius: 4px;
+  font-size: 1rem;
+  font-family: inherit;
+}
+
+input:focus {
+  outline: none;
+  border-color: #4285f4;
+}
+
+button {
+  padding: 0.75rem 1.5rem;
+  background-color: #4285f4;
+  color: white;
+  border: none;
+  border-radius: 4px;
+  font-size: 1rem;
+  font-family: inherit;
+  cursor: pointer;
+  transition: background-color 0.2s;
+}
+
+button:hover {
+  background-color: #357ae8;
+}
+
+button:active {
+  background-color: #2a65c8;
+}
+
+.error-list {
+  color: red;
+  font-size: 0.875rem;
+  margin: 0.25rem 0 0 0;
+  padding-left: 0;
+  list-style-position: inside;
+}
+
+.error-list p {
+  margin: 0;
+}

adev/src/content/tutorials/playground/4-signal-forms/src/main.ts

@@ -0,0 +1,77 @@
+import {bootstrapApplication} from '@angular/platform-browser';
+import {Component, signal, ChangeDetectionStrategy} from '@angular/core';
+// @ts-ignore There's a known issue with type support in the playground editor for signal forms
+import {form, Field, required, email, debounce, submit} from '@angular/forms/signals';
+
+interface LoginData {
+  email: string;
+  password: string;
+}
+
+@Component({
+  selector: 'app-root',
+  template: `
+    <form (submit)="onSubmit($event)">
+      <div>
+        <label>
+          Email:
+          <input type="email" [field]="loginForm.email" />
+        </label>
+
+        @if (loginForm.email().invalid()) {
+          <ul class="error-list">
+            @for (error of loginForm.email().errors(); track $index) {
+              <li>{{ error.message }}</li>
+            }
+          </ul>
+        }
+      </div>
+
+      <div>
+        <label>
+          Password:
+          <input type="password" [field]="loginForm.password" />
+        </label>
+
+        @if (loginForm.password().invalid()) {
+          <div class="error">
+            @for (error of loginForm.password().errors(); track $index) {
+              <p>{{ error.message }}</p>
+            }
+          </div>
+        }
+      </div>
+
+      <button type="submit">Log In</button>
+    </form>
+  `,
+  styleUrl: 'main.css',
+  imports: [Field],
+  changeDetection: ChangeDetectionStrategy.OnPush,
+})
+export class LoginApp {
+  loginModel = signal<LoginData>({
+    email: '',
+    password: '',
+  });
+
+  loginForm = form(this.loginModel, (schemaPath) => {
+    debounce(schemaPath.email, 500);
+    required(schemaPath.email, {message: 'Email is required'});
+    email(schemaPath.email, {message: 'Enter a valid email address'});
+    debounce(schemaPath.password, 500);
+    required(schemaPath.password, {message: 'Password is required'});
+  });
+
+  onSubmit(event: Event) {
+    event.preventDefault();
+    submit(this.loginForm, async () => {
+      // Perform login logic here
+      const credentials = this.loginModel();
+      console.log('Logging in with:', credentials);
+      // e.g., await this.authService.login(credentials);
+    });
+  }
+}
+
+bootstrapApplication(LoginApp);