docs: Overhaul contributor infrastructure and add GitHub templates

[pradeepkch6-ai]

Description

This PR improves the contributor onboarding experience by overhauling the repository's contributor infrastructure.

The existing CONTRIBUTING.md was highly focused on the regression-corpus contract (which is critical), but lacked guidance on environment setup, local testing, and static analysis. I have expanded the documentation to extract the existing workflows defined in composer.json (composer ecs, composer stan, composer test) into a clear onboarding guide.

The original regression-corpus instructions have been strictly preserved in a dedicated section.

Additionally, this PR introduces:

• A Bug Report template (requesting PHP/Laravel/Engine versions)
• A Feature Request template
• A Pull Request template with a self-review checklist mapping to the CI requirements.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

[rmcdaniel]

Thank you for this contribution. The expanded contributor setup, testing, and regression-corpus guidance is useful and is being incorporated from this exact revision.

We cannot merge the repository-local issue templates because this organization uses centralized structured issue forms; adding local templates here would replace that intake surface. The pull-request checklist, branch reference, release examples, and product positioning also need a small revision before landing.

We are preparing that corrected integration while preserving your contribution attribution. I am leaving this PR open until the resulting change has landed and required checks are green, then I will follow up here with the incorporated result and close it cleanly.

[rmcdaniel]

Completed in f0e03c9181a4 on v2.

No package release was required for this source-only change.

Required public qualification build (php.yml) passed in run 31860885021.