feat(cli): add --max-total-size flag to audit cleanup

[christine-at-datadog]

Closes #1818

Summary

Adds a --max-total-size <MB> flag to nono audit cleanup: sorts sessions oldest-first (the same discovery/sort path the command already uses) and removes sessions until the remaining total is under the given size, using the existing per-session disk_size already computed for each SessionInfo. Purely additive — behavior without the flag is unchanged.

Deliberately does not compose with --older-than as an AND filter in the same invocation; a caller wanting size-bounded pruning of recent-but-large sessions should pass --max-total-size alone, since combining it with --older-than would exclude the very sessions the size bound exists to catch. Noted in the flag's help text.

Files changed

• crates/nono-cli/src/cli.rs — new max_total_size: Option<u64> field on AuditCleanupArgs, plus a unit test (test_audit_cleanup_max_total_size).
• crates/nono-cli/src/audit_commands.rs — size-based pruning pass in cmd_cleanup, after the existing --keep filtering; respects --dry-run.

Testing

• New unit test covers: total already under budget (no-op) and total over budget (prunes oldest until under).
• cargo test, cargo clippy -- -D warnings -D clippy::unwrap_used, and cargo fmt --check all pass locally.

Agent Compliance Check

• I am not prohibited from contributing under this policy
• An issue already exists (audit cleanup: add a size-bounded pruning mode (--max-total-size) #1818)
• I described my intent and approach in the issue discussion
• I reviewed repository coding and security rules for the affected area
• I provided required attribution for reused or adapted code (none reused/adapted — new logic only)
• I did not use forbidden patterns such as unwrap/expect
• I used NonoError where required
• I validated and canonicalized all relevant paths
• This PR matches the approved or disclosed issue scope

This contribution was prepared with the assistance of an AI coding agent (Claude Code), reviewed and submitted by a human maintainer of the downstream project referenced in the linked issue.

[github-actions]

PR Review Summary

Size

Metric	Value
Lines added	+108
Lines removed	-1
Total changed	109
Classification	Medium (50–300 lines)

Affected crates

• crates/nono-cli — CLI changes. Verify argument parsing, flag documentation, and UX behaviour across supported platforms.

Blast radius — Contained

This PR touches: source code

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_{Updated automatically on each push to this PR.}

[nogent-nolabs-ai]

nogent code review

1 potential bug identified.

_{Automated code + security review. CI already covers clippy, rustfmt, tests, cargo-audit and commit-lint.}

[SequeI]

Hi!

Thanks for the PR, let's also add documentation for this new flag so users are aware of the option, and let me know if the nogent comments have been addressed. Overall looks good though, thanks!

[SequeI]

lgtm, thanks Christine!