agent: TodosPanel/InboxPanel flyouts + header pills

New Preact `SidePanel` drawer — deliberately not the shared
`<hive-side-panel>` shadow-DOM custom element, same rationale as
StatusChips' Badge/Dropdown. Drops that element's drag-to-resize +
localStorage width persistence for this first slice (fixed width via
CSS); reuses agent.css's existing `.agent-inbox`/`.inbox-*`/
`.side-panel-empty` content classes verbatim, only the drawer chrome
itself is new (SidePanel.css). Kept mounted regardless of open/closed
state (toggles the `open` prop) rather than conditionally rendered, so
the slide/fade CSS transitions actually fire on both open and close.

- InboxPanel: renders `state.inbox` (already polled by useAgentState)
  + a "mark all read" action — plain `fetch()` to the dashboard's
  `/api/agent/{name}/mark-all-read` (JSON response, same as app.js;
  unlike pause/resume this one doesn't need a form-submit workaround).
- TodosPanel: new `useTodos` hook (same 4s poll cadence as app.js's
  `refreshTodos`) + bulk select/mark-done via `api/todos/mark-done`.
- Both destructive-but-recoverable actions use a new `useConfirmClick`
  two-click-arm hook instead of the old shadow-DOM `themedConfirm`
  modal — lighter weight, no backdrop/dialog machinery needed for a
  "did you mean to click that" nudge.
- HeaderPill: the inbox/todos count triggers in the header's right
  cluster; Header.tsx gained a `pills` slot for them (mirrors the old
  markup's `.agent-header-pills` third column).
- types.ts: added `InboxRow`/`TodoRow`, mirroring
  `hive_sh4re::inbox::{InboxRow, LooseEnd}` (todo variant only —
  `/api/todos` never returns the others).

Screenshot-verified against a mock server exercising both panels.

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

@@ -0,0 +1,104 @@
+// <TodosPanel> — content rendered inside <SidePanel> for the todos
+// flyout. "mark done" POSTs to this agent's own backend
+// (`api/todos/mark-done`, same-origin), unlike InboxPanel's cross-agent
+// mark-all-read.
+import { useState } from 'preact/hooks';
+import type { TodoRow } from '../types.js';
+
+export interface TodosPanelProps {
+  todos: TodoRow[];
+  onCleared: () => void;
+}
+
+function fmtAge(seconds: number): string {
+  if (seconds < 60) return `${seconds}s`;
+  if (seconds < 3600) return `${Math.floor(seconds / 60)}m`;
+  if (seconds < 86400) return `${Math.floor(seconds / 3600)}h`;
+  return `${Math.floor(seconds / 86400)}d`;
+}
+
+export function TodosPanel({ todos, onCleared }: TodosPanelProps) {
+  const [checked, setChecked] = useState<Set<number>>(new Set());
+  const [status, setStatus] = useState('');
+  const [busy, setBusy] = useState(false);
+
+  function toggle(id: number) {
+    setChecked((prev) => {
+      const next = new Set(prev);
+      if (next.has(id)) next.delete(id);
+      else next.add(id);
+      return next;
+    });
+  }
+
+  async function markDone() {
+    const ids = [...checked];
+    if (!ids.length) return;
+    setBusy(true);
+    setStatus('marking…');
+    try {
+      const resp = await fetch('api/todos/mark-done', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+        body: `ids=${encodeURIComponent(ids.join(','))}`,
+      });
+      if (resp.ok) {
+        setStatus('✓ marked done');
+        setChecked(new Set());
+        onCleared();
+      } else {
+        setStatus(`failed: ${await resp.text()}`);
+      }
+    } catch (err) {
+      setStatus(`failed: ${err instanceof Error ? err.message : String(err)}`);
+    } finally {
+      setBusy(false);
+    }
+  }
+
+  if (!todos.length) {
+    return <p class="side-panel-empty">no todos — all subsystem queues are clear.</p>;
+  }
+
+  const allChecked = todos.length > 0 && todos.every((t) => checked.has(t.id));
+
+  return (
+    <div class="agent-inbox">
+      <div class="inbox-mark-all-row">
+        <button
+          type="button"
+          class="inbox-mark-all-btn"
+          onClick={() => setChecked(allChecked ? new Set() : new Set(todos.map((t) => t.id)))}
+        >
+          {allChecked ? 'select none' : 'select all'}
+        </button>
+        <button type="button" class="inbox-mark-all-btn" onClick={markDone} disabled={busy || checked.size === 0}>
+          ✓ mark done
+        </button>
+        <span class="inbox-mark-status">{status}</span>
+      </div>
+      <ul>
+        {todos.map((t) => {
+          const cbId = `todo-cb-${t.id}`;
+          const label = t.source ? `${t.subsystem} · ${t.source}` : t.subsystem;
+          return (
+            <li key={t.id}>
+              <input
+                type="checkbox"
+                id={cbId}
+                class="todo-cb"
+                checked={checked.has(t.id)}
+                onChange={() => toggle(t.id)}
+              />{' '}
+              <label for={cbId} class="inbox-from">
+                {label}
+              </label>{' '}
+              <span class="inbox-ts">{fmtAge(t.age_seconds)} ago</span>
+              <div class="inbox-body">{t.summary}</div>
+            </li>
+          );
+        })}
+      </ul>
+    </div>
+  );
+}