Normalize title field from visible task text

[Farahani1]

Summary

• Add extract_visible_task_title() to derive the task title from the checkbox text before #task.
• During normalization, overwrite or add [title:: ...] so it matches that visible task text.
• Preserve the existing field ordering behavior and unknown-field preservation.

Example

- [ ] do one training session before Ace exam #task ... [title:: reserve one training session before Ace exam]

normalizes to:

- [ ] do one training session before Ace exam #task ... [title:: do one training session before Ace exam]

Notes

No automated test suite was present in the repository, so I validated the change by inspecting the updated normalization logic.