ci: add trunk

[jamesnrokt]

Background

• This repo had no static analysis or formatting enforcement. Adding Trunk aligns it with other ROKT SDKs (sdk-android-source, sdk-ios-source, rokt-ux-helper-*).

What Has Changed

• Added .trunk/trunk.yaml with 15 linters, a custom mparticle-api-key-check rule to detect committed API keys, path/linter ignores, and git hook actions
• Added trunk-check as the first required job in the pull request workflow (blocks pr-notify)
• Added .github/workflows/trunk-upgrade.yml to auto-upgrade linter versions on the 1st of each month

Screenshots/Video

• N/A

Checklist

• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• I have added tests that prove my fix is effective or that my feature works.
• I have tested this locally.

Additional Notes

• yamllint is disabled (matches sdk-android-source)
• CHANGELOG.md is excluded from markdownlint as its format intentionally violates MD001/MD024/MD025
• Example/Pods, Example/Podfile.lock, RNExample/Gemfile* are excluded from all linters

Reference Issue (For employees only. Ignore if you are an outside contributor)

• N/A

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