## 1. Refactor note submission

- [x] 1.1 Extract note submission logic from `runAdd` into a shared `submitNote` helper (multipart POST, duplicate detection, output formatting)

## 2. Root command shorthand

- [x] 2.1 Add `Args: cobra.ArbitraryArgs` and `RunE` to the root command — join args into a note string, call `submitNote`; show help when no args
- [x] 2.2 Add `--tags` flag on the root command for note tagging

## 3. Rename add → addfile

- [x] 3.1 Rename command from `add` to `addfile` (`Use: "addfile <path>"`)
- [x] 3.2 Remove `--note`, `--title`, and `--type` flags from the command
- [x] 3.3 Add extension validation for single file uploads — reject unsupported extensions with a clear error listing supported types

## 4. Documentation and verification

- [x] 4.1 Update README.md usage section: show `kb "text"` shorthand, rename `add` references to `addfile`
- [x] 4.2 Verify build compiles, `kb --help` and `kb addfile --help` show expected output