chore(PulseBand): remove generated Keil artifacts while preserving HEX snapshot

.gitignore

@@ -1,8 +1,10 @@
 # Keil user/session and generated outputs
 *.uvguix.*
 *.uvoptx
-firmware/OBJ/
-firmware/USER/Listings/
+firmware/OBJ/*
+!firmware/OBJ/.gitkeep
+firmware/USER/Listings/*
+!firmware/USER/Listings/.gitkeep
 *.bak
 *.tmp
 .DS_Store

README.md

@@ -93,6 +93,8 @@ For detailed hardware list and connection instructions, please refer to [hardwar
    - Connect ST-Link to STM32 development board
    - Click `Flash` → `Download` or press `F8`
 
+**Build outputs:** Keil writes generated objects to `firmware/OBJ/` and listings to `firmware/USER/Listings/`. These build artifacts are intentionally ignored. A previously committed `Template.hex` snapshot is preserved under [`firmware/prebuilt/`](firmware/prebuilt/); its hardware compatibility has not been independently verified. For a reproducible firmware image, rebuild from source in Keil.
+
 ### Mobile APP Usage
 
 1. **Install APP**

README_zh-CN.md

@@ -92,6 +92,8 @@
    - 连接 ST-Link 到 STM32 开发板
    - 点击 `Flash` → `Download` 或按 `F8`
 
+**构建产物管理：** Keil 生成的对象文件位于 `firmware/OBJ/`，Listing 文件位于 `firmware/USER/Listings/`，均不再纳入版本控制。原仓库中的 `Template.hex` 快照已保存在 [`firmware/prebuilt/`](firmware/prebuilt/)，**尚未对其硬件兼容性进行独立验证**；建议使用 Keil 从源码重新编译固件。
+
 ### 手机 APP 使用
 
 1. **安装 APP**

docs/REPOSITORY-STRUCTURE.md

@@ -9,13 +9,15 @@ This file documents the **actual source layout** and highlights why the Keil pro
 | `firmware/FWLIB/` | STM32F10x standard peripheral library |
 | `firmware/HARDWAR/` | Sensor and peripheral drivers (MAX30102, ADXL345, OLED and others) |
 | `firmware/SYSTEM/` | Board/system support code |
-| `firmware/OBJ/` | Existing tracked Keil build outputs; ignored for new files |
+| `firmware/OBJ/` | Keil-generated build directory (placeholder retained, outputs ignored) |
+| `firmware/USER/Listings/` | Keil-generated listing directory (placeholder retained, outputs ignored) |
+| `firmware/prebuilt/Template.hex` | Historical HEX snapshot; not an independently verified release |
 | `hardware/` | PCB designs, circuit files and reference materials |
 | `mobile-app/` | Android application release and project assets |
 | `docs/` | Hardware, development and contribution guides |
 
 Open `firmware/USER/Template.uvprojx` using Keil µVision. Its project settings reference relative source directories; changing firmware folder names can break the build. Firmware paths therefore remain untouched pending a build verification.
 
-The `.gitignore` prevents *new* Keil machine-specific files and build products from being tracked, but does **not** delete already committed files. Existing outputs can be cleaned separately after comparing them with release assets.
+This cleanup removes previously tracked Keil object, listing and user-session files from the **current repository tree**, while retaining history and a separate HEX snapshot for reference. It does not rewrite or shrink Git history. `.gitignore` prevents regenerated objects from being recommitted and preserves the directory placeholders.
 
 This educational prototype is **not a medical diagnostic device**; listed sensor/accuracy claims should be independently validated before clinical use.