refactor: convert 0x01_uart_cbm and 0x02_blink_cbm to bare-metal Inc/Src structure

- Restructure flat files into Inc/ (headers) and Src/ (sources)
- Replace constants.h with rp2350.h register layer (datasheet-verified)
- Add full Doxygen docstrings on all files, functions, and structs
- Replace build.bat/clean.bat with cross-platform Makefile
- Fix GPIO_IN offset (0x004), XOSC COUNT offset (0x10), SRAM size (520K)
- Rename blink_* API to led_* (name after peripheral, not feature)
- Build outputs to build/ directory
- Cross-platform .vscode configs (Windows/macOS/Linux)

drivers/0x01_uart_cbm/.vscode/c_cpp_properties.json

@@ -3,7 +3,27 @@
         {
             "name": "ARM GCC",
             "includePath": [
-                "${workspaceFolder}/**"
+                "${workspaceFolder}/Inc/**"
+            ],
+            "defines": [
+                "__GNUC__",
+                "__ARM_ARCH_8M_MAIN__",
+                "__ARMCC_VERSION"
+            ],
+            "compilerPath": "${userHome}/.pico-sdk/toolchain/14_2_Rel1/bin/arm-none-eabi-gcc",
+            "compileCommands": "${workspaceFolder}/compile_commands.json",
+            "cStandard": "c11",
+            "cppStandard": "c++17",
+            "intelliSenseMode": "gcc-arm",
+            "compilerArgs": [
+                "-mcpu=cortex-m33",
+                "-mthumb"
+            ]
+        },
+        {
+            "name": "ARM GCC (Windows)",
+            "includePath": [
+                "${workspaceFolder}/Inc/**"
             ],
             "defines": [
                 "__GNUC__",
@@ -22,4 +42,4 @@
         }
     ],
     "version": 4
-}
+}