Add photos and datasheet; correct wiring and protocol docs

The 20L203 input is RS-232 (reference build uses a MAX3232), it runs on
5-24 V, and it boots in non-scrolling overwrite mode.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

components/samsung_vfd/samsung_vfd.h

@@ -14,10 +14,7 @@ namespace samsung_vfd {
 
 static const char *const TAG = "samsung_vfd";
 
-// Control bytes, taken from older Arduino sketches that drove this display.
-// The one known to work only ever used ESC @ and 0x0C; 0x0B ("home") came
-// from an earlier test sketch. That sketch also sent 0xB0, which is left out:
-// it is most likely a printable glyph, not a command.
+// Control bytes, see section 5.4 of docs/20L203DA12-datasheet.pdf.
 static const uint8_t CMD_ESC = 0x1B;
 static const uint8_t CMD_INIT = 0x40;   // ESC @  -> reset / init display
 static const uint8_t CMD_CLEAR = 0x0C;  // FF     -> clear screen (cursor to home)