test: add process PTY backup restore acceptance (M6.5.2)

[KeyffMS]

Implements M6.5.2 from #26: process-level PTY acceptance for the production Backup / Diff / Restore path added in #77.

Scope:

• launches the real vfd-lantern process in a controlled terminal PTY;
• launches the real lantern-sim process and connects product traffic through its PTY/Modbus RTU boundary;
• approves the exact local profile hash and arms writes through the production TUI;
• captures and persists a complete backup through the production runtime;
• creates a valid differing source backup, loads it through the TUI, captures the fresh pre-restore backup and prepares the semantic restore plan;
• verifies exact restore confirmation is operator-visible;
• wrong confirmation executes exactly zero FC06/FC16 writes;
• correct confirmation reaches the physical PTY once; the intentionally read-only base simulator returns IllegalFunction and the product stops after exactly one FC06 with zero retry;
• reconstructs the current terminal screen for process assertions, matching the established connection-process harness rather than matching raw ANSI stream history;
• the process test asserts the real Backup screen is rendered, not the historical placeholder;
• the new acceptance is part of scripts/ci/quality.sh and therefore runs under the normal Debian 13 amd64 coverage gate.

Successful device-side write/apply semantics remain covered by the write-capable #27 conformance PTY runtime; this item proves the real product process/TUI/composition/BusActor boundary reaches the same guarded restore path.

Final acceptance: CI #1023 / run 34572013073 completed successfully on exact head d875af1d9b1a9df85a68c21e3a3bde39e0744ec2; quality/coverage, process acceptance and supply-chain gates are green.

Refs #25
Refs #26