v0.1.2-ke-fixes

Added

• Print-status: filename label, dynamic ETA, auto-dismiss when done.
• Extruder: non-blocking heat, auto-extrude on reaching target temp, busy spinner.
• KUtils::notify_toast transient feedback and a gcode_script response-callback overload (groundwork
  for later guided flows).

Changed

• CI builds only the Ender-3 V3 KE release asset; added a self-hosted cross-toolchain Docker image.
• Busy spinners normalized to 80×80.
• User-focused README rewrite + in-repo wiki.
• Reverted the v0.1.1 "LED on home / Fine Tune in Tune tab" change.