`OverflowMenu.tsx`/`.css` were deleted (rebuild button removed outright,
dashboard link moved into `MetaNav`), but `agent.css` still carried the
whole trigger+popover+item rule set — grepped the entire `agent`
package, none of these classnames appear in any current markup.
Also fixed three tombstone comments elsewhere in the file that pointed
at the now-also-deleted `.overflow-item-*` classes as "where it moved
to" — they'd have dangled once those rules were gone too. And two stale
doc claims caught in the same sweep: `docs/web-ui/agent.md` still listed
`OverflowMenu.tsx` in the header's component tree and described "the
overflow menu" as a live effort-picker location.
cd339af91b