fix: simplify ESP32-C3 workshop OLED sketch

[w1ne]

Summary

• simplify the ESP32-C3 workshop sketch to the two SSD1306 OLED modules only
• keep one Arduino source with WORKSHOP_OLED_HEIGHT selecting 128x64 vs 128x32 init/geometry
• replace thin one-pixel segment strokes with filled seven-segment clock digits

Verification

• PlatformIO build: WORKSHOP_OLED_HEIGHT=64
• PlatformIO build: WORKSHOP_OLED_HEIGHT=32
• flashed rebuilt 0.96 OLED image to /dev/cu.usbmodem21201 with esptool; hash verified
• serial capture from real ESP32-C3: ESP32-C3 Display Workshop + WORKSHOP_TICK at 1.000s cadence