## Context

The root cobra command in `client/cmd/root.go` uses `cobra.ArbitraryArgs` and its `RunE` handler to catch any arguments not matching a subcommand. Currently, any non-empty args are joined and submitted as a note. This means a single mistyped word (e.g., `kb infow` instead of `kb info`) silently creates a junk note in the knowledge base.

## Goals / Non-Goals

**Goals:**
- Prevent single bare words from being silently ingested as notes
- Provide a clear error message that helps the user correct their input
- Preserve the multi-word implicit note shorthand (`kb remember to update dns`)

**Non-Goals:**
- Detecting "close matches" to real commands (fuzzy matching / did-you-mean)
- Changing how quoted strings work at the shell level (we can't detect quotes after shell expansion)

## Decisions

### Guard on argument count in RunE

When `len(args) == 1`, reject with an error message instead of submitting as a note. When `len(args) > 1`, continue treating as implicit note shorthand.

**Rationale**: This is the simplest reliable heuristic. The shell strips quotes before cobra sees args, so we cannot distinguish `kb "singleword"` from `kb singleword`. However, single-word notes are rare in practice, and the error message tells the user how to work around it (use multiple words or the full note workflow). Multi-word input is almost certainly intentional note text, not a mistyped command.

**Alternative considered**: Checking against a list of known subcommand names — rejected because it wouldn't catch typos of commands we don't know about and adds maintenance burden.

## Risks / Trade-offs

- **Single-word notes no longer work via shorthand** → Users must use `kb add --note "singleword"` or include additional words. This is an acceptable trade-off since single-word notes are uncommon and the error message is clear.
- **Shell quote stripping means we can't be perfect** → `kb "my note"` with exactly one word after quote removal will be rejected. This is a known limitation but very rare in practice.