chore: LICENSE (MIT), Cargo.toml metadata, gitignore firmware, display cleanup

- Add MIT LICENSE file (Stephen Waits <steve@waits.net>)
- Add Cargo.toml: authors, license, description, repository, readme, keywords
- Gitignore /firmware (built binaries don't belong in VCS)
- Display task: use DisplayState::new() for reset, handle watch/brightness errors

.gitignore

@@ -1,5 +1,6 @@
 /target
 /vendor
+/firmware
 src/board/mod.rs
 __pycache__/
 .hypothesis/