REVA v3.3beta20d — locked-show OLED UI

BASELINE
- Rebuilt from known-good beta19.
- Pulse engine unchanged.
- Timer1 carrier unchanged.
- Timer2 packet executor unchanged.
- EEPROM structure/version kept compatible with beta19.

IMPORTANT CHANGE FROM FAILED beta20/beta20c
- Removed risky pixel marquee / big-font scroller.
- Startup stays normal.
- No automatic marquee at boot.
- After a real operator change is saved to EEPROM, OLED enters stable LOCKED SHOW mode.
- Any button change exits LOCKED SHOW mode immediately.

LOCKED SHOW MODE
Cycles through simple large graphical cards:
1. LOCKED family + pulse/gap bars
2. packet scope
3. rate / packet duration
4. density
5. segment map

Purpose:
- Make the small OLED easier to read after tuning is finished.
- Avoid the refresh/restart problem seen in beta20/beta20c.
