fix(honeypot): avoid auto-block on probe-only sessions

[maiconburn]

Summary

• avoid auto-block for probe-only honeypot sessions (no auth attempts and no shell commands)
• compute session duration using real elapsed time instead of auth-attempt heuristic
• add explicit Telegram note for probe-only sessions
• add unit tests for auto-block gating and duration rounding

Why

Probe-only scans were generating debriefs with duration 0s / commands 0 and still reporting auto-block as if there had been attacker interaction. This PR makes the behavior explicit and less noisy for operators.

Validation

• cargo check -p innerwarden-agent
• cargo test -p innerwarden-agent --quiet