delete the combobox instead of giving it anchor semantics

audit m7 ranked this medium because "every caller inherits the opaque click". there
are no callers. nothing has imported Combobox since the initial commit, there is no
barrel that re-exports it, and nothing anywhere sets `href` on a SelectOption — so the
navigate, the separator that only appeared for href options, and the href field on both
declarations of the type were all unreachable.

writing anchor semantics into a component that is never rendered is building, not
fixing. the Command primitives it used stay; AIHarnessesSection needs them.

src/apps/CLAUDE.md

@@ -19,7 +19,6 @@ Location: `src/workspaces/components/`
 Built on top of shadcn primitives:
 - `Avatar.tsx` - User avatars
 - `Card.tsx` - Custom card wrapper
-- `Combobox.tsx` - Searchable select
 - `ColorPicker.tsx` - Color selection
 - `DataTable/` - Table with sorting, filtering, pagination (see below)
 - `Dialogs/` - Common dialog patterns