feat: Add process package to monorepo

- Add `sal-process` package for cross-platform process management.
- Update workspace members in `Cargo.toml`.
- Mark process package as complete in MONOREPO_CONVERSION_PLAN.md
- Remove license information from `mycelium` and `os` READMEs.

mycelium/README.md

@@ -108,7 +108,3 @@ cargo test -- --nocapture
 - `base64` - Message encoding
 - `tokio` - Async runtime
 - `rhai` - Scripting support
-
-## License
-
-Apache-2.0