Simplify install.sh: remove unused prompts, fix config keys

Remove poll_interval_sec, cfs_autosync (removed from codebase).
Replace moonraker_url + separate port prompt with single printer_url
(IP only). Write clean config with current keys. Update branding to
CFSync.

filament_diameter_mm is kept — used by mm_to_g() for Spoolman reporting.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>