feat: hide the pi status bar indicator while keeping ponytail active (#324) (#544)

Add getHideStatus() to the shared config resolver: PONYTAIL_HIDE_STATUS (any
truthy value; 0/false/empty mean don't hide) or config.hideStatus === true, with
BOM-stripped config reads. The pi extension caches it at init and re-reads on
session_start, and syncStatus() returns early when set, so the indicator is
suppressed while the ruleset still injects every turn.

Reconciles #511 and #328: takes #328's caching and ruleset-stays-active test,
#511's BOM-safe config read, a stricter env check (0/false do not hide), and
drops #328's writeDefaultMode change which already landed in #514.

Closes #324

Co-authored-by: dhedhialy <91044156+dhedhialy@users.noreply.github.com>
Co-authored-by: sanmaxdev <46221775+sanmaxdev@users.noreply.github.com>