agent: fill the inbox/todos header pill to match the rest of the cluster

HeaderPill used the bordered/transparent .hive-pill shape while every
other chip in .agent-header-pills (StatusChips, MetaNav's trigger) is
@hive/shared's filled Badge (.ui-badge) -- the one visibly hollow pill
in a row of filled ones. Restyled .header-pill with .ui-badge's own
values (filled --purple-dim background, no border, matching radius/
padding/hover) instead of a new shape, and dropped hive-pill from the
markup since it no longer describes what this component looks like.

frontend/packages/agent/src/agent.css

@@ -320,25 +320,31 @@ h2, h3 {
 }
 
 /* Header pill — inbox / loose-ends triggers. Compact, count-prominent.
-   Markup carries `hive-pill` alongside `header-pill` (shared pill.css
+   Filled to match every OTHER chip in `.agent-header-pills`
-   supplies border/radius/padding/font-size/letter-spacing; `display`
+   (StatusChips' alive/state/model/effort/pause, MetaNav's 🔗 trigger —
-   is the one thing overridden here, to `inline-flex`, for the icon+
+   all `@hive/shared`'s `Badge`, an `.ui-badge` filled pill) — no
-   label+count row layout — see pill.css's own note on that). */
+   `hive-pill` on the markup any more (its bordered/transparent shape
+   is what made this one read as visually distinct from its neighbours;
+   values below are `.ui-badge`/`.ui-badge-interactive`'s own, not a
+   new shape). `display: inline-flex` (not Badge's default) for the
+   icon+label+count row this component alone needs. */
 .header-pill {
-  background: transparent;
+  background: var(--purple-dim);
-  border-color: var(--purple-dim);
+  border: none;
+  border-radius: 1em;
+  padding: 0.15em 0.6em;
+  min-height: 2.75em;
+  padding-inline: 0.8em;
   color: var(--fg);
   font-family: inherit;
   display: inline-flex;
   align-items: center;
   gap: 0.4em;
   cursor: pointer;
-  transition: border-color 0.15s ease, box-shadow 0.15s ease, color 0.15s ease;
+  transition: background 0.15s ease, color 0.15s ease;
 }
 .header-pill:hover {
-  border-color: var(--purple);
+  background: var(--border);
-  color: var(--purple);
-  box-shadow: 0 0 10px -2px var(--purple);
 }
 .header-pill-icon { font-size: 1.05em; line-height: 1; }
 .header-pill-label { color: var(--muted); }

frontend/packages/agent/src/components/HeaderPill.tsx

@@ -1,9 +1,10 @@
 // <HeaderPill> — the inbox/todos flyout triggers in the header's right
-// cluster. Reuses agent.css's existing `.hive-pill.header-pill…` rules
+// cluster. Reuses agent.css's existing `.header-pill…` rules (loaded
-// (loaded globally) — same "layout is a like-for-like port, the
+// globally), styled to match `@hive/shared`'s filled `Badge` pill —
-// component model is the change" approach as Header.tsx. Hidden
+// every other chip in the same cluster is one — not the bordered
-// (renders nothing) at count 0, matching the old page's `pill.hidden =
+// `.hive-pill` shape (mara: "inbox badge looks different from all the
-// count === 0`.
+// other ones"). Hidden (renders nothing) at count 0, matching the old
+// page's `pill.hidden = count === 0`.
 export interface HeaderPillProps {
   kind: 'inbox' | 'todos';
   icon: string;
@@ -15,7 +16,7 @@ export interface HeaderPillProps {
 export function HeaderPill({ kind, icon, label, count, onClick }: HeaderPillProps) {
   if (count === 0) return null;
   return (
-    <button type="button" class={`hive-pill header-pill header-pill-${kind}`} onClick={onClick} title={`open ${label} flyout`}>
+    <button type="button" class={`header-pill header-pill-${kind}`} onClick={onClick} title={`open ${label} flyout`}>
       <span class="header-pill-icon" aria-hidden="true">
         {icon}
       </span>