fix: update Output block to match TerminalProgressRenderer format

[juhgiyo]

Summary

• Replace aspirational checkmark output in the "Output" section with format matching the real TerminalProgressRenderer from cli/src/strawpot/progress.py
• New output shows: session start, delegation stages with role names and durations, session complete line
• Keeps existing <span class="s"> CSS styling on checkmark characters

Closes strawpot/strawpot#510

Acceptance Criteria

• Output block matches TerminalProgressRenderer format (Session started, > Delegating to..., ✓ completed, ✓ Session complete)
• Stage names use real role slugs (implementer, code-reviewer)
• Durations are realistic (1m 23s, 47s, 2m 34s)
• HTML renders correctly — build passes
• demo-script.yaml command (strawpot run) is consistent with run command from #509

Test plan

• npm run build passes
• Visual inspection of <pre><code> block structure

🤖 Generated with Claude Code

[juhgiyo]

Closing as redundant — PR #72 already includes these output block changes along with the Under the Hood audit. See #72 for the combined update.