Initial commit: LSPi (LiangShanPi) project

GD32F470ZGT6 based project with full peripheral support:
- SDRAM (W9825G6KH) via EXMC
- LCD NT35510 (480x800) via EXMC NOR/PSRAM
- Flash (W25Q64) via SPI
- UART (USART0) debug console
- LED indicators
- CMSIS-DAP debug interface
- CMake + ARM GCC toolchain build system

.gitignore

@@ -0,0 +1,45 @@
+# ============ 构建产物 ============
+build/
+cmake-build-*/
+out/
+output/
+
+# ============ IDE / 编辑器 ============
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+.DS_Store
+Thumbs.db
+
+# ============ Python 缓存 ============
+__pycache__/
+*.pyc
+*.pyo
+
+# ============ 编译中间文件 ============
+*.o
+*.d
+*.obj
+*.dep
+*.map
+*.su
+*.lst
+
+# ============ 烧录相关临时文件 ============
+openocd_temp.cfg
+flash_temp.cfg
+
+# ============ 可执行文件/库文件 ============
+*.elf
+*.hex
+*.bin
+*.exe
+
+# ============ 第三方库备份/临时 ============
+libs/thirdparty/GD32F4xx_Official/
+libs/thirdparty/GD32F4xx_AddOn_Temp/
+
+# ============ 配置文件本地修改 ============
+/config/*.local.*