v0.3.20

feat(gui): Probleme frecvente button + smarter probe report

Lessons from today's field session where NAK-on-every-baud×dialect
finally turned out to be an unverified cash register (no ANAF
activation). Built that + other common failure modes into the app so
future users self-diagnose faster:

1. bridge/probe.py — format_report() now detects the "all NAK"
   pattern and promotes the most-likely cause (neverified register)
   to the top of the recommendation. Checklist also gained:
     • physical display readout interpretation
     • "try a different USB cable" tip (charge-only cables mimic this)
     • Datecs PrintProxy shutdown steps
     • paper-stuck / C-key recovery
     • proprietary Datecs tool cross-check

2. bridge/gui.py — new "❓ Probleme frecvente" button opens a
   standalone scrollable Troubleshooting dialog. Covers the 8
   top patterns we hit today (NAK everywhere, 90s flap, Save doesn't
   persist, status dots gray, 'Conexiune PC' display, wrong port,
   wrong baud, CAM0x codes, dezinstalare). Also:
     • Dedicated _show_scroll_text helper — replaces tk.messagebox
       for long reports. Text is selectable + has a "Copiază tot"
       button so users can paste into a support ticket.
     • Probe button now uses the scrollable dialog too, so nothing
       gets cut off on a low-resolution screen.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>