Split Nano firmware into modules

- config.h: all constants and debug defines
- command_parser.h/.cpp: CommandParser class, one method per command
- settings.h/.cpp: EEPROM flip time storage
- main.cpp: setup/loop and the periodic full redraw only
- Full redraw now checks frameEnded() after the serial buffer is drained
- Drop the SPI/Adafruit_I2CDevice include workaround (not needed)

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

CLAUDE.md

@@ -42,6 +42,8 @@ See README.md for the overview.
 
 ## Nano serial parser (`src/nano/main.cpp`)
 
+- Files: `main.cpp` (setup/loop, refresh), `config.h` (all constants and debug
+  defines), `command_parser.*` (protocol, one method per command), `settings.*` (EEPROM).
 - Line based and non-blocking: bytes are collected into a 64-character buffer and a
   command runs when `\n` arrives. Bitmap (`B`) pixel data is the exception. It is drawn
   while it arrives, so it can be longer than the buffer. Keep `loop()` free of busy-waits.
@@ -53,7 +55,7 @@ See README.md for the overview.
 - The Nano only replies `READY` (at boot) and `ERR: ...`. There is no per-frame
   acknowledgement. Whether the Nano's TX is wired to the ESP's RX is unconfirmed, so every
   wait for a reply needs a timeout.
-- To test the parser without hardware, compile `main.cpp` with g++ (Strawberry Perl
+- To test the parser without hardware, compile all `src/nano/*.cpp` files with g++ (Strawberry Perl
   provides it at `C:\Strawberry\c\bin`) and mock headers for `Arduino.h`, `EEPROM.h` and
   `BROSE9323.h`.