ci: add workflow_dispatch trigger and improve PR review workflow

[Copilot]

Overview

PR #4's CI checks cannot be re-triggered after the clippy fixes landed via PR #5. This updates pr-review.yml to support manual re-runs and incorporates the workflow improvements from PR #4.

Changes:

• Add workflow_dispatch trigger — enables manual re-runs from Actions → PR Review → Run workflow
• Update header comment references to kebab-case filenames (review-checklist.md, rust-crypto-review.md)
• Relax commit-message check: only HEAD commit must follow conventional format (hard fail); intermediate commits warn only
• Skip PR-context jobs (commit-message-check, pr-description-check) during workflow_dispatch runs
• Fix concurrency group to use github.run_id fallback for non-PR triggers
• Guard intermediate commit loop against single-commit PRs

Type of Change

• Bug Fix
• New Feature
• Documentation Update
• Refactor
• 🔧 Configuration/CI

Checklist

• Code follows the project's style guidelines (cargo fmt passes)
• No Clippy warnings (cargo clippy -- -D warnings passes)
• Unit tests have been added or modified (cargo test passes)
• Documentation has been updated (cargo doc --no-deps passes)
• No sensitive information (keys, secrets, PII) is exposed
• Commit messages follow the conventional commit format (e.g., feat:, fix:, chore:)

Related Issues

Relates to PR #4, PR #5.

Additional Notes

After merge, PR #4's checks can be re-triggered by either re-running failed jobs from the GitHub UI or closing/reopening the PR. The workflow_dispatch trigger also enables standalone runs from the Actions tab for ad-hoc validation.

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