feat: Add support for PAYLOAD_TYPE_GRP_DATA

Docs changes are to reflect how it is currently in fw

This adds ability to send datagram data to everyone in channel

docs/companion_protocol.md

@@ -257,31 +257,56 @@ Bytes 34-49: Secret (16 bytes)
 
 ---
 
-### 5. Send Channel Message
+### 5. Send Channel Text Message
 
-**Purpose**: Send a text message to a channel.
+**Purpose**: Send a plain text message to a channel.
 
 **Command Format**:
 ```
 Byte 0: 0x03
-Byte 1: 0x00
+Byte 1: Text Type
 Byte 2: Channel Index (0-7)
 Bytes 3-6: Timestamp (32-bit little-endian Unix timestamp, seconds)
-Bytes 7+: Message Text (UTF-8, variable length)
+Bytes 7+: UTF-8 text bytes (variable length)
 ```
 
 **Timestamp**: Unix timestamp in seconds (32-bit unsigned integer, little-endian)
 
+**Text Type**:
+- Must be `0x00` (`TXT_TYPE_PLAIN`) for this command.
+
 **Example** (send "Hello" to channel 1 at timestamp 1234567890):
 ```
 03 00 01 D2 02 96 49 48 65 6C 6C 6F
 ```
 
-**Response**: `PACKET_MSG_SENT` (0x06) on success
+**Response**: `PACKET_OK` (0x00) on success
 
 ---
 
-### 6. Get Message
+### 6. Send Channel Data Datagram
+
+**Purpose**: Send binary datagram data to a channel.
+
+**Command Format**:
+```
+Byte 0: 0x3E
+Byte 1: Data Type (`txt_type`)
+Byte 2: Channel Index (0-7)
+Bytes 3-6: Timestamp (32-bit little-endian Unix timestamp, seconds)
+Bytes 7+: Binary payload bytes (variable length)
+```
+
+**Data Type / Transport Mapping**:
+- `0xFF` (`TXT_TYPE_CUSTOM_BINARY`) is the custom-app binary type.
+- `0x00` (`TXT_TYPE_PLAIN`) is invalid for this command.
+- Values other than `0xFF` are reserved for official protocol extensions.
+
+**Response**: `PACKET_OK` (0x00) on success
+
+---
+
+### 7. Get Message
 
 **Purpose**: Request the next queued message from the device.
 
@@ -304,7 +329,7 @@ Byte 0: 0x0A
 
 ---
 
-### 7. Get Battery and Storage
+### 8. Get Battery and Storage
 
 **Purpose**: Query device battery voltage and storage usage.
 
@@ -446,7 +471,7 @@ Byte 1: Channel Index (0-7)
 Byte 2: Path Length
 Byte 3: Text Type
 Bytes 4-7: Timestamp (32-bit little-endian)
-Bytes 8+: Message Text (UTF-8)
+Bytes 8+: Payload bytes
 ```
 
 **V3 Format** (`PACKET_CHANNEL_MSG_RECV_V3`, 0x11):
@@ -458,9 +483,14 @@ Byte 4: Channel Index (0-7)
 Byte 5: Path Length
 Byte 6: Text Type
 Bytes 7-10: Timestamp (32-bit little-endian)
-Bytes 11+: Message Text (UTF-8)
+Bytes 11+: Payload bytes
 ```
 
+**Payload Meaning**:
+- If `txt_type == 0x00`: payload is UTF-8 channel text.
+- If `txt_type != 0x00`: payload is binary (for example image/voice fragments) and must be treated as raw bytes.
+  For custom app datagrams sent via `CMD_SEND_CHANNEL_DATA`, use `txt_type == 0xFF`.
+
 **Parsing Pseudocode**:
 ```python
 def parse_channel_message(data):
@@ -477,11 +507,17 @@ def parse_channel_message(data):
     path_len = data[offset + 1]
     txt_type = data[offset + 2]
     timestamp = int.from_bytes(data[offset+3:offset+7], 'little')
-    message = data[offset+7:].decode('utf-8')
+    payload = data[offset+7:]
+    if txt_type == 0:
+        message = payload.decode('utf-8')
+    else:
+        message = None
     
     return {
         'channel_idx': channel_idx,
+        'txt_type': txt_type,
         'timestamp': timestamp,
+        'payload': payload,
         'message': message,
         'snr': snr if packet_type == 0x11 else None
     }
@@ -489,7 +525,7 @@ def parse_channel_message(data):
 
 ### Sending Messages
 
-Use the `SEND_CHANNEL_MESSAGE` command (see [Commands](#commands)).
+Use `CMD_SEND_CHANNEL_TXT_MSG` for plain text, and `CMD_SEND_CHANNEL_DATA` for binary datagrams (see [Commands](#commands)).
 
 **Important**: 
 - Messages are limited to 133 characters per MeshCore specification
@@ -510,7 +546,7 @@ Use the `SEND_CHANNEL_MESSAGE` command (see [Commands](#commands)).
 | 0x03  | PACKET_CONTACT             | Contact information           |
 | 0x04  | PACKET_CONTACT_END         | End of contact list           |
 | 0x05  | PACKET_SELF_INFO           | Device self-information       |
-| 0x06  | PACKET_MSG_SENT            | Message sent confirmation     |
+| 0x06  | PACKET_MSG_SENT            | Direct message sent confirmation |
 | 0x07  | PACKET_CONTACT_MSG_RECV    | Contact message (standard)    |
 | 0x08  | PACKET_CHANNEL_MSG_RECV    | Channel message (standard)    |
 | 0x09  | PACKET_CURRENT_TIME        | Current time response         |
@@ -675,7 +711,7 @@ def parse_self_info(data):
     return info
 ```
 
-**PACKET_MSG_SENT** (0x06):
+**PACKET_MSG_SENT** (0x06, used by direct/contact send flows):
 ```
 Byte 0: 0x06
 Byte 1: Route Flag (0 = direct, 1 = flood)
@@ -737,7 +773,8 @@ BLE implementations enqueue and deliver one protocol frame per BLE write/notific
      - `DEVICE_QUERY` → `PACKET_DEVICE_INFO`
      - `GET_CHANNEL` → `PACKET_CHANNEL_INFO`
      - `SET_CHANNEL` → `PACKET_OK` or `PACKET_ERROR`
-     - `SEND_CHANNEL_MESSAGE` → `PACKET_MSG_SENT`
+     - `CMD_SEND_CHANNEL_TXT_MSG` → `PACKET_OK` or `PACKET_ERROR`
+     - `CMD_SEND_CHANNEL_DATA` → `PACKET_OK` or `PACKET_ERROR`
      - `GET_MESSAGE` → `PACKET_CHANNEL_MSG_RECV`, `PACKET_CONTACT_MSG_RECV`, or `PACKET_NO_MORE_MSGS`
      - `GET_BATTERY` → `PACKET_BATTERY`
 
@@ -809,7 +846,7 @@ command = build_channel_message(channel_index, message, timestamp)
 
 # 2. Send command
 send_command(rx_char, command)
-response = wait_for_response(PACKET_MSG_SENT)
+response = wait_for_response(PACKET_OK)
 ```
 
 ### Receiving Messages