ci: align commitlint config across pre-commit and CI

[nielspardon]

Summary

The PR title check workflow generated its own throwaway commitlint config inline, while .commitlintrc.js (used by the local pre-commit hook) maintained a separate, stricter rule set. The two diverged, so local commits were validated differently than PR titles in CI.

This makes .commitlintrc.js the single source of truth, mirroring the substrait repo:

• .commitlintrc.js now extends @commitlint/config-conventional (which supplies the same type list, case, and length rules that were previously hand-maintained), loosens the body/footer length rules, and ignores dependabot messages — including the Updates the requirements on … to permit the latest version. pattern that substrait has but we were missing.
• .github/workflows/pr_title.yaml no longer generates a config inline. It checks out the repo and runs commitlint against the checked-in config. Under pull_request_target, actions/checkout defaults to the trusted base branch, so a PR cannot supply its own commitlint rules.
• .pre-commit-config.yaml gains additional_dependencies: ['@commitlint/config-conventional'] so the local commit-msg hook can resolve the now-extended config (the hook only bundles @commitlint/cli).

Notes

Local commits now use the same loosened length rules as CI rather than the old strict 100-char limits — that is the intended convergence, since CI was the effective authority anyway. The commitizen prompt block was dropped to match substrait's config.

Closes #640

🤖 Generated with Claude Code

[nielspardon]

This should make the configuration consistent. If I read #640 correctly then we may actually remove the pre-commit configuration for commitlint since Ben suggests to not check commits but PR title / description only.