Escape-room mechanic: the retro phone can call the players on its own
and tell them a story when they pick up.
Approach: a story_ring_task rings at a random 15-30 min interval (only
when the line is idle and a story pack is on the SD). Picking up routes
through enter_story_from_ring(), which silences the bell and launches a
random story via plip_gamebook_begin_random() straight into the gamebook
state — no menu. If nobody answers within 1 min the bell stops and the
next ring is rescheduled; hanging up mid-ring also silences it.
The whole feature is gated behind CONFIG_PLIP_AUTO_RING (default n), so
the phone stays silent unless explicitly enabled in menuconfig. The hook
pickup paths (raw SLIC poll + debounced edge) mirror the existing NPC
incoming-call handling, which is unreliable while the bell rings.
clement