- Move opensbi and qemu from git submodules to Makefile-managed clones
  with blobless clone + checkout + git apply patches
- Add patches/opensbi-amp.patch (hart routing, PIE fix, IPI forwarding,
  CLINT S/U access, next_addr)
- Add patches/qemu-uart1.patch (second UART at 0x10002000)
- Remove run.sh (replaced by make run), STATUS.md (outdated), tests/
- Add apps/user-test-ipc: Rust userspace IPC test for StarryOS
- Add make targets: setup, user-test, install
- Update docs/IPC-DESIGN.md to reflect current implementation
- Update README.md, .gitignore, Cargo.toml