Fix Mainsail livestats: wrong progress percentage and remaining time

[HK-Moebius]

The Mainsail enhanced app (added in #642) shows wrong values while a print is running. This affects every Klipper/Moonraker printer, not a specific model.

Problems

1. Progress is always 0% or 1%.
   Moonraker reports display_status.progress as a fraction between 0.0 and 1.0. The app rounds that value directly without multiplying by 100, so a print at 45% is shown as 0%, and anything from 50% onwards as 1%.

2. The remaining time is unrelated to the print.
   toolhead.estimated_print_time is not the estimated duration of the print job. It is Klipper's internal print time clock, which keeps running since Klipper started. Subtracting print_stats.print_duration from it produces a value that depends on the printer's uptime, so the "Finish" value grows the longer the printer has been powered on.

Changes

• Multiply the progress by 100. If display_status.progress is not set (no M73 in the G-code), fall back to virtual_sdcard.progress.
• Calculate the remaining time from the slicer estimate in the file metadata (/server/files/metadata, estimated_time) minus print_stats.print_duration. This is the same data Mainsail itself uses for its slicer-based estimate.
• If no slicer estimate is available, extrapolate from progress and elapsed print time.
• Query virtual_sdcard instead of toolhead, since toolhead is no longer needed.
• Use null-coalescing for the status fields so a missing object does not cause a PHP notice.

The output keys (completed_pct, estimated, state) and the presentation are unchanged, so livestats.blade.php does not need to change.

Testing

Tested with a Klipper/Moonraker printer (Prusa Pro HT90) during a running print. Progress and remaining time now match what Mainsail shows.