Add full protobuf schema and generated code

docs/host_protocol_rebuild.md

@@ -0,0 +1,109 @@
+# Host Protocol Rebuild
+
+## Goal
+
+Use protobuf as the single protocol definition source.
+
+This stage fixes two earlier mistakes:
+
+- payload encode/decode should not be hand-written in COM
+- the outer CDC frame should also be part of the schema
+
+## Current schema
+
+Files:
+
+- `KeyBorad/proto/keyboard.proto`
+- `KeyBorad/proto/keyboard.options`
+
+## Design
+
+### 1. Outer frame is part of protobuf
+
+The outer CDC frame is described as:
+
+- `CdcFrame`
+
+Fields:
+
+- `head1`
+- `head2`
+- `payload_length`
+- `type`
+- `payload`
+- `checksum`
+
+### 2. Business body is part of protobuf
+
+The business payload is described as:
+
+- `CdcPacketBody`
+
+Supported messages:
+
+- `HelloReq`
+- `HelloRsp`
+- `Bitmap`
+- `FunctionKeyEvent`
+- `LedState`
+- `TimeSync`
+- `ThemeRgb`
+- `Ack`
+- `Error`
+
+### 3. Transport split
+
+- CDC sends `CdcFrame`
+- GATT sends `CdcPacketBody`
+
+## Why this is the chosen direction
+
+- one full schema instead of half schema
+- no repeated hand-written payload parsing
+- easier to teach layer responsibilities
+- easier to align host and firmware
+
+## Current blocker
+
+`protoc.exe` is not present in `3rdParty`, but the machine has an available
+protobuf compiler binary at:
+
+```text
+C:\Program Files\Lenovo\AIAgent\Modules\RAG\_internal\torch\bin\protoc.exe
+```
+
+## Completed nodes
+
+### Node 1: full schema definition
+
+Files:
+
+- `KeyBorad/proto/keyboard.proto`
+- `KeyBorad/proto/keyboard.options`
+
+Implemented behavior:
+
+- outer frame moved into protobuf as `CdcFrame`
+- business body moved into protobuf as `CdcPacketBody`
+- all current message types included in one schema
+
+### Node 2: generated C++ protobuf code
+
+Files:
+
+- `KeyBorad/generated/cpp/keyboard.pb.h`
+- `KeyBorad/generated/cpp/keyboard.pb.cc`
+
+Implemented behavior:
+
+- generated from the full protocol schema
+- ready to be used by the later thin COM wrapper
+
+## Next step
+
+Stop expanding hand-written typed payload parsing.
+
+The next COM implementation step should use:
+
+- generated `keyboard.pb.h/.cc`
+- a thin wrapper that connects `QByteArray` with generated protobuf messages