[05] Bill & coin (eSSP) emulator screen

[jvwaldrich0]

Task 05 of 16 — these are sequential, do them in order.

Previous: #7 · Next: #9

Port target: cloudpark-toolkit (Go) → this repo (Rust). Reference paths below are relative to that repo.

Goal

The bill & coin (eSSP) emulator screen, driven by the existing src/bill_emulator.rs + src/serial_bridge.rs.

Scope

• Start the pty bridge and show the slave path (/dev/pts/N) so the host app can connect to it.
• Device selector: bill validator / coin acceptor / hopper (whatever DeviceState already supports).
• Actions: insert note (value picker), insert coin, reject, enable/disable, payout.
• Live log pane of the eSSP traffic: command byte → response, and the poll event stream (READ, CREDIT, STACKING, STACKED, REJECTED, DISPENSED, …) decoded to names, not raw hex only.
• Status line: enabled/disabled, cashbox, last event, credit total.

Reference

This repo: src/bill_emulator.rs, src/essp_protocol.rs, src/serial_bridge.rs, src/bin/bill_emulator.rs

Done when

• The screen prints a working pty path and an eSSP host completes SYNC → SETUP → POLL against it.
• Inserting a note produces the READ → CREDIT → STACKING → STACKED sequence in the log.
• CRC failures are logged, not fatal.