Add Badge + Dropdown Preact components, demo on swarm-ui /components

New shared Preact primitives for the per-agent terminal redesign:

- Badge (@hive/shared/badge.js): a labelled status pill. Plain <span>
  when static (e.g. "alive"), a real <button> with a disclosure caret
  when given onClick (e.g. opens a Dropdown, or toggles itself in
  place). Same component either way so a status row reads as one
  consistent set of badges regardless of which are interactive.
- Dropdown (@hive/shared/dropdown.js): a small option list anchored
  directly under whatever opened it (no portal, no native <dialog> —
  see the file comment for why). Closes on outside click or Escape.

This is the fix for the design guide's own named anti-example: the
agent page's model/effort pickers live in the overflow menu while the
current model/effort only show as a disconnected chip. Badge+Dropdown
composed together is that control moved inline, next to what it shows.

Demoed on swarm-ui's /components page: all Badge tones, a label-prefixed
badge, an interactive badge that opens a Dropdown (model-picker shape),
and an interactive badge that toggles itself (pause/resume shape).

Both packages build + tsc --noEmit clean.

frontend/packages/swarm-ui/src/pages/ComponentsPage.css

@@ -42,3 +42,10 @@
   font-size: 0.8em;
   color: var(--muted);
 }
+/* Anchor for a Badge + the Dropdown it opens (@hive/shared) — Dropdown
+   positions `absolute` against this box, see Dropdown.css's file-top
+   comment. */
+.components-badge-anchor {
+  position: relative;
+  display: inline-block;
+}