feat(lab3): signed commits + gitleaks pre-commit hook

[Mukhin-I]

Goal

Configure SSH commit signing, wire gitleaks into a pre-commit hook to block accidental secret commits.

Changes

• .pre-commit-config.yaml — gitleaks v8.27.2 + detect-private-key + check-added-large-files hooks
• submissions/lab3.md — signing config, verified badge, blocked commit evidence, tune-out tradeoffs

Testing

• git log --show-signature -1 shows Good "git" signature for i.muhin@innopolis.university
• Commit 3379c6c shows green Verified badge on GitHub
• gitleaks blocked submissions/leak-attempt.txt with RuleID github-pat
• Fake secret cleaned up — not committed to repo

Artifacts & Screenshots

• submissions/lab3.md — full write-up
• .pre-commit-config.yaml — hook config
• GitHub commit page showing Verified badge: (3379c6c)

---

Checklist

• Title follows feat(labN): <topic>
• No secrets or large temp files committed
• submissions/labN.md exists

PR Cheklist

• Task 1 — SSH signing configured + Verified badge on commit
• Task 2 — .pre-commit-config.yaml + gitleaks demonstrably blocking
• Bonus — filter-repo rewrite practice documented