activity: select-only multi-client filter

the freetype client field is gone. the picker is a select-only menu of known clients with multi-select, chips for the active set, and a 32-client cap shared with the server. the api accepts a comma-separated client list and filters any-of with bound parameters. the trigger carets come from phosphor icons, newly adopted. bundle budget rises to 900000 bytes for the picker and the icon dependency.

admin/src/ui/Select.tsx

@@ -10,6 +10,7 @@
  * models an id converts on both edges.
  */
 
+import { CaretDown } from "@phosphor-icons/react";
 import * as stylex from "@stylexjs/stylex";
 import {
 	Button,
@@ -83,6 +84,7 @@ const styles = stylex.create({
 		whiteSpace: "nowrap",
 	},
 	chevron: {
+		display: "inline-flex",
 		color: colors.textMuted,
 	},
 	description: {
@@ -155,7 +157,7 @@ export default function Select({
 			<Button className={() => stylex.props(base, block, styles.trigger, shared.focusRing).className ?? ""}>
 				<SelectValue className={() => stylex.props(styles.value).className ?? ""} />
 				<span aria-hidden="true" {...stylex.props(styles.chevron)}>
-					▾
+					<CaretDown size={12} />
 				</span>
 			</Button>
 			{description !== undefined && (