refactor: move the Somfy frame codec into SomfyFrame.cpp

The command and protocol enums, somfy_frame_t and its encode/decode
methods, and both translateSomfyCommand overloads move verbatim out of
Somfy.cpp/Somfy.h, which now include SomfyFrame.h.  The codec doesn't
depend on the radio, storage or network, so on its own it can be unit
tested on the PC.

decodeFrame(somfy_rx_t*) stays in Somfy.cpp since it reads the RSSI
from the CC1101.  No behaviour change.

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

src/SomfyFrame.h

@@ -0,0 +1,70 @@
+#ifndef SOMFY_FRAME_H
+#define SOMFY_FRAME_H
+#include <Arduino.h>
+
+// The RTS frame codec and command names.  Kept free of the radio, storage and
+// network so it can be unit tested on the PC (pio test -e native).
+enum class radio_proto : byte { // Ordinal byte 0-255
+  RTS = 0x00,
+  RTW = 0x01,
+  RTV = 0x02,
+  GP_Relay = 0x08,
+  GP_Remote = 0x09
+};
+enum class somfy_commands : byte {
+    Unknown0 = 0x0,
+    My = 0x1,
+    Up = 0x2,
+    MyUp = 0x3,
+    Down = 0x4,
+    MyDown = 0x5,
+    UpDown = 0x6,
+    MyUpDown = 0x7,
+    Prog = 0x8,
+    SunFlag = 0x9,
+    Flag = 0xA,
+    StepDown = 0xB,
+    Toggle = 0xC,
+    UnknownD = 0xD,
+    Sensor = 0xE,
+    RTWProto = 0xF, // RTW Protocol
+    // Command extensions for 80 bit frames
+    StepUp = 0x8B,
+    Favorite = 0xC1,
+    Stop = 0xF1
+};
+String translateSomfyCommand(const somfy_commands cmd);
+somfy_commands translateSomfyCommand(const String& string);
+
+struct somfy_rx_t;
+struct somfy_frame_t {
+    bool valid = false;
+    bool processed = false;
+    bool synonym = false;
+    radio_proto proto = radio_proto::RTS;
+    int rssi = 0;
+    byte lqi = 0x0;
+    somfy_commands cmd;
+    uint32_t remoteAddress = 0;
+    uint16_t rollingCode = 0;
+    uint8_t encKey = 0xA7;
+    uint8_t checksum = 0;
+    uint8_t hwsync = 0;
+    uint8_t repeats = 0;
+    uint32_t await = 0;
+    uint8_t bitLength = 56;
+    uint16_t pulseCount = 0;
+    uint8_t stepSize = 0;
+    uint8_t rawCmd = 0;
+    void print();
+    void encode80BitFrame(byte *frame, uint8_t repeat);
+    byte calc80Checksum(byte b0, byte b1, byte b2);
+    byte encode80Byte7(byte start, uint8_t repeat);
+    void encodeFrame(byte *frame);
+    void decodeFrame(byte* frame);
+    void decodeFrame(somfy_rx_t *rx);
+    bool isRepeat(somfy_frame_t &f);
+    bool isSynonym(somfy_frame_t &f);
+    void copy(somfy_frame_t &f);
+};
+#endif