Enforce commit messages reference GitHub issue (#<num>) via pre-commit

[sugan0tech]

Summary

• Add a commit-msg hook to require a GitHub issue reference like #123 in commit messages (subject or body).

Rationale

• Branch naming already encodes the issue ID, but requiring a reference in the commit message improves traceability in logs and when squash-merging.
• Keeps Conventional Commits via Commitizen while nudging contributors to add a footer (e.g., ‘Refs #’ or ‘Closes #’).

Scope

• Add a local pre-commit commit-msg hook that checks for /#[0-9]+/ in the commit message.
• Exempt merge and release commits.
• Document the rule in CONTRIBUTING.md.

Acceptance Criteria

• Commits without # (except allowed exemptions) fail locally.
• Docs mention the requirement and show examples.
• PR merges leave no broken commit flows.

[sugan0tech]

Additional scope: Add a pre-commit line-count check for changed files.\n- Warn when a file exceeds 300 lines (up to 450).\n- Block the commit when any file exceeds 450 lines.\n\nThis helps keep files small and focused while still allowing flexibility for moderate increases.