The UI only noticed a removed card when some user action ran a real card
command (e.g. Check status); /api/status is a cached-state read that kept
returning the old card, and _handle_card_disconnect() did not clear
app.card/rs.
- start_card_monitor() registers a pyscard CardObserver for our reader;
it only polls SCardGetStatusChange (no APDU, no connection, no extra
process), and on removal sets server.card_present=False and calls
_handle_card_disconnect() under _CARD_LOCK
- /api/status now exposes connected (session usable) and card_present
(physically inserted) and masks card/profile/atr/selection when not
connected; _CARD_CONNECTED is initialized from card presence instead of
being unconditionally True
- the 2s UI poll includes /api/status; on disconnect it switches to the
existing 'No card detected. Insert card and click Equip' state, or the
new 'Card inserted — press Equip' hint when the card is back; the old
_hadData heuristic is gone
Tests for the observer (filtering, removal, insertion) and the UI state
transitions. SW cache v90 -> v91.
