feat(instructions): add Symfony/PHP development instructions

[vlahanas]

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• My contribution adds a new instruction, prompt, or chat mode file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, or chat mode with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.

---

Description

This PR adds a new instruction file, php-symfony.instructions.md, focused on Symfony development aligned with the framework's official best practices.

It provides Copilot with specific context on Symfony’s core philosophy, emphasizing autowiring, constructor injection, and the use of PHP attributes for routing and Doctrine mapping. The file is structured to steer the model away from legacy anti-patterns—such as "fat" controllers, manual container access, and the use of bundles for application code—and towards standard modern practices like using AssetMapper for web assets, Symfony Secrets for sensitive configuration, and thin, service-oriented architecture.

---

Type of Contribution

• New instruction file.
• New prompt file.
• New chat mode file.
• New collection file.
• Update to existing instruction, prompt, chat mode, or collection.
• Other (please specify):

---

By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[Copilot]

Pull request overview

This PR introduces comprehensive Symfony development instructions to guide GitHub Copilot in generating code aligned with official Symfony Best Practices. The instruction file covers modern Symfony development patterns including autowiring, dependency injection, attribute-based configuration, and emphasizes avoiding legacy anti-patterns.

Key Changes:

• New instruction file providing Symfony-specific development standards
• README documentation updated with the new instruction entry

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
instructions/php-symfony.instructions.md	Comprehensive instruction file covering Symfony best practices across controllers, services, Doctrine, Twig templates, forms, security, testing, and general guidelines. Properly formatted with required front matter and applies to PHP, YAML, XML, and Twig files.
docs/README.instructions.md	Added table entry for the new Symfony instruction file with installation badges, inserted in alphabetical order between Swift MCP Server and Taming Copilot entries.