fix(progress): ignore code-fenced status markers

[sylvesterkaczmarek]

Summary

Keep Markdown examples and quoted code from being reported as live scan progress or worker dispatch state.

Fixes #525.

Problem

Progress parsing currently toggles a single boolean for every line beginning with three backticks. A valid four-backtick outer fence can therefore be closed incorrectly by a shorter three-backtick run inside it, exposing a quoted progress marker as live state.

Worker-status parsing has no fence handling at all, so a marker inside an ordinary fenced example is accepted directly.

Changes

• share one fenced-line filter between scan-progress and worker-status parsing;
• track the opening fence character and run length instead of toggling a boolean;
• close only with the same marker character and a run at least as long as the opener;
• handle both backtick and tilde Markdown fences;
• add focused regressions for a four-backtick outer fence, fenced worker-status examples, tilde fences, and genuine markers after the fence closes.

Validation

The branch is based on current upstream main (99c85613b0c4b8202b33dfbd80f41884fb9eac11) and is not behind it. Full repository tests cannot be run in this execution environment because the repository cannot be cloned here; pushed-head CI remains required.

Risk

Low. JSON marker validation is unchanged. The change only removes marker-looking lines while they are inside Markdown fenced code blocks.