Sync Output Cleanup

[EspenAlbert]

Summary

Improves CLI output readability when syncing to multiple destinations:

• Replaces the flat "Syncing to {name}..." line with a visual separator/header block using box-drawing characters
• Prints the destination header before skip-checks so users see which destination is being evaluated even when it is skipped
• Adds explicit status echo for skipped and no-change destinations so the header block is never left hanging
• Includes the PR URL in the update_pr_body log message for easier debugging
• Adds a visual phase header for auto-merge so it is clearly separated from the sync phase
• Adds dest-name context and polling progress logging to auto-merge (enable_auto_merge, wait_for_merge)
• Includes PR URLs in the auto-merge summary table
• Adds logger.warning in get_pr_url on failure (consistent with other gh CLI wrappers)