Ports swarm-ui's `SettingsMenu` (mara: "agent terminal page should get
the settings panel from swarm ui as well") — same shape as `MetaNav`
already in this header: a `Badge` icon trigger ("⚙"), popover, close on
outside-click/Escape.
`theme-apply.ts` + `settings-storage.ts` are near-verbatim ports of
swarm-ui's own (duplicated rather than moved into `@hive/shared` for
this pass — lower risk than reworking swarm-ui's imports in the same
change). Defaults the stored override to 'dark', not 'system', for the
same reason as swarm-ui's own default flip: `prefers-color-scheme` has
no real "unset" value, so 'system' silently reads as light for anyone
who's never touched an OS dark-mode toggle.
Motion NOT ported — agent has no animation gated behind `data-motion`
yet, so that plumbing would have nothing to control.
Verified end-to-end: default dark on a fresh load, and an explicit
localStorage override to 'light' correctly re-themes the whole page via
the existing `colors.css` `:root[data-theme='light']` block (already
shipped, previously only reachable from swarm-ui).
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