Update SPFx tutorials: Migrate from gulp to heft commands

[Ashlesha-MSFT]

Category

• [ x] Content fix

Related issues

• fixes SPFx Docs Update for Heft toolchain: build-client-side-web-parts-with-angular-1-x.md #10583

What's in this Pull Request?

• Updated all build commands from deprecated gulp serve/gulp build to modern heft start/heft build
• Removed outdated Office UI Fabric references as it's no longer supported
• Refreshed screenshots to show current Heft build output and modern SPFx project structure
• Upgraded code samples and fixed TypeScript compilation issues for current SharePoint Framework versions

[learn-build-service-prod]

PoliCheck Scan Report

The following report lists PoliCheck issues in PR files. Before you merge the PR, you must fix all severity-1 and severity-2 issues. The AI Review Details column lists suggestions for either removing or replacing the terms. If you find a false positive result, mention it in a PR comment and include this text: #policheck-false-positive. This feedback helps reduce false positives in future scans.

✅ No issues found

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[learn-build-service-prod]

Learn Build status updates of commit 5ff22b4:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/images/ng-intro-app-folder.png	✅Succeeded	View
docs/images/ng-intro-hide-finished-tasks.png	✅Succeeded	View
docs/images/ng-intro-project-visual-studio-code.png	✅Succeeded	View
docs/images/ng-intro-property-pane-toggle-browser.png	✅Succeeded	View
docs/images/ng-intro-property-pane-toggle.png	✅Succeeded	View
docs/images/ng-intro-workbench-office-ui-fabric.png	✅Succeeded	View
docs/images/ng-intro-yeoman-generator.png	✅Succeeded	View
docs/spfx/web-parts/guidance/build-client-side-web-parts-with-angular-1-x.md	✅Succeeded	View

For more details, please refer to the build report.