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>

CLAUDE.md

@@ -1,7 +1,7 @@
 # CLAUDE.md
 
-ESPHome external component for a Samsung 2×20 serial VFD (5 V TTL, 9600 8N1,
-write-only). It is consumed from git by an ESPHome server through
+ESPHome external component for a Samsung 20L203 2×20 serial VFD (RS-232
+input, 9600 8N1, write-only). It is consumed from git by an ESPHome server through
 `external_components: source: github://...`, so the layout must stay
 `components/samsung_vfd/` at the repo root.
 
@@ -13,6 +13,8 @@ write-only). It is consumed from git by an ESPHome server through
   and the templated action classes.
 - `components/samsung_vfd/samsung_vfd.cpp`: the shadow buffer, word wrap,
   UTF-8 → single-byte sanitising and `flush_()`.
+- `docs/20L203DA12-datasheet.pdf`: the command set (section 5.4), jumpers,
+  wiring and the character tables. Check it before adding protocol features.
 - `examples/samsung-vfd.yaml`: the full reference device config. It pulls the
   component from GitHub; for local work, switch to the commented
   `type: local, path: ../components` source.
@@ -27,8 +29,13 @@ write-only). It is consumed from git by an ESPHome server through
   `last_payload_` so the next flush retransmits.
 - Text sent to the display is one byte per character; always pass it through
   `sanitize_()`.
-- Keep the protocol constants in `samsung_vfd.h`. Only `ESC @`, `0C` and `0B`
-  are known to work.
+- Keep the protocol constants in `samsung_vfd.h`. The display boots in
+  overwrite mode: the cursor wraps from the end of line 1 to line 2 and from
+  the end of line 2 back home, and nothing scrolls. A full-screen redraw is
+  therefore `0B` plus `rows × cols` characters.
+- The RXD input is RS-232. The reference build uses a MAX3232 (no inversion
+  in config); a directly wired ESP32 pin needs `inverted: true` on the UART TX
+  pin.
 
 ## Checking changes