Enhance VS Code setup, fix dynamic ELF path, pin dependencies, and expand README

• Use dynamic ELF path in launch.json (${workspaceFolderBasename}.elf)
• Remove hardcoded ARM toolchain path for portability
• Pin FetchContent dependencies to specific commits
• Add Python tools (cbor2, intelhex) setup instructions
• Document VS Code configuration files and workflow
• Add OpenOCD, SVD, toolchain, and key management documentation