Refresh contributor docs, add PR template, code of conduct, and code standards

[lancepioch]

Fixes the broken \vendor\bin paths in contributing.md (now composer pint / composer phpstan), refreshes the dev environment setup (Herd-first with SQLite, frontend asset build, verified artisan commands), documents the pre-PR checks and the CLA Assistant signing flow, and links the user docs.

Adds .github/PULL_REQUEST_TEMPLATE.md, a Contributor Covenant 2.1 code_of_conduct.md (contact: team@pelican.dev, cross-linked from contributing.md and security.md), and code-standards.md covering Pint, Larastan (including the forbidden app()/resolve() rule), Pest suites, the API contract freeze, and codebase conventions.

The supported-versions wording in security.md is left to #2567; labels and good-first-issue seeding are handled outside this PR. The CLA is already enforced by cla.yaml, so no workflow changes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Advanced

Run ID: 17db448d-ac63-4a06-8955-95868a21da4b

📥 Commits

Reviewing files that changed from the base of the PR and between fdb519e and c9c477e.

📒 Files selected for processing (5)

• .github/PULL_REQUEST_TEMPLATE.md
• code-standards.md
• code_of_conduct.md
• contributing.md
• security.md

Included review availability: Your plan provides up to 8 included reviews per hour; 5 remain after this review.

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📝 Walkthrough

Walkthrough

The changes add contribution standards, setup and validation guidance, a pull request checklist, a Contributor Covenant code of conduct, and a link between vulnerability reporting and the code of conduct.

Changes

Contribution Documentation

Layer / File(s)	Summary
Contribution workflow and standards .github/PULL_REQUEST_TEMPLATE.md, code-standards.md, contributing.md	The project documents coding standards, development setup, local validation commands, CLA requirements, and pull request checklist items.
Conduct and vulnerability reporting code_of_conduct.md, contributing.md, security.md	The project adds a Contributor Covenant code of conduct and links contribution and vulnerability-reporting guidance to it.

Priority: ⬇️ Low

Merge Risk: ⚪ Minimal · up to c9c47

This documentation-only change has no remaining material merge risk.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly summarizes the main changes: contributor documentation updates and additions of a pull request template, code of conduct, and code standards.
Description check	✅ Passed	The description accurately explains the documentation refresh, new governance files, development setup updates, cross-links, CLA process, and out-of-scope items.

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