[TASK] Lint job (swift-format or swiftlint)

[kirich1409]

Context

Add linting stage. Decide between swift-format (Apple official) and swiftlint; document choice.

Acceptance criteria

• Linter chosen, config committed.
• Runs as a separate CI job; failure blocks PR merge.

Files to touch (estimate)

best-effort estimate; agent refines during implementation

Implementation notes

n/a

Dependencies

• Blocked by [TASK] Base GitHub Actions build workflow #22

Safety checklist

See .github/ISSUE_TEMPLATE/task.yml — tick applicable invariants in the issue if any destructive path is touched.

Definition of Done

• Acceptance criteria satisfied and verifiable
• Tests added or updated
• No build / lint / test regressions
• Self-review against research-report invariants
• Code review approved