Update firmware documentation and agent guidance

variants/versapad/variant.h

@@ -1,6 +1,6 @@
 #pragma once
 
-// VersaPad v2 – SAMD21G18A Custom Variant
+// VersaPad v2 – SAMD21G17D Custom Variant
 // Arduino pin assignments for the custom PCB
 
 #define ARDUINO_SAMD_VARIANT_COMPLIANCE 10610
@@ -24,14 +24,14 @@
 // attachInterrupt() then internally looks up ulExtInt via g_APinDescription.
 
 // ─── Button Matrix ────────────────────────────────────────────────────────────
-// Columns (driven LOW one at a time)
+// Columns (inputs with external pull-ups; read LOW for a pressed switch)
 #define PIN_COL0   (4u)   // PB10  – also encoder SW column
 #define PIN_COL1   (3u)   // PA11
 #define PIN_COL2   (2u)   // PA10
 #define PIN_COL3   (1u)   // PA09
 #define PIN_COL4   (0u)   // PA08
 
-// Rows (read with internal pull-up)
+// Rows (idle high-Z; driven LOW one at a time during scanning)
 #define PIN_ROW0   (5u)   // PB11
 #define PIN_ROW1   (6u)   // PA12
 #define PIN_ROW2   (7u)   // PA13