feat(cli): add optional message timestamps between exchanges

[dieutx]

Summary

• Add display.show_timestamps config option (default: false)
• When enabled, prepends HH:MM:SS to the separator line between user/assistant exchanges
• Useful for tracking how long tasks take during long CLI sessions

Enable in ~/.hermes/config.yaml:

display:
  show_timestamps: true

Example output:

14:32:05 ────────────────────────────────────

Closes #1569

Test plan

• Timestamps shown when show_timestamps: true in config
• No change when config option is absent or false
• Uses datetime.now().strftime("%H:%M:%S") for consistent formatting
• Run pytest tests/ to confirm no regressions

[teknium1]

Closing — we've reviewed the batch of 30 PRs submitted in ~36 hours and found multiple duplicates of other contributors' work, at least one no-op (identical bytes to main), and no tests or filled checklists. We appreciate the intent, but please focus on quality over quantity: check for existing PRs before submitting, verify your diff is real, add tests, and fill out the PR template. If you have a specific fix you've tested and verified, we're happy to review it.