feat(dashboard): add repo filter, sort order, and max results controls to Token Cost page

Three reactive dropdowns below the Token Cost heading:
- Filter by repo: client-side filter via 3-level chain resolution
- Sort by: Tokens Total (default), Tokens In, Out, Event Count, Most Recent
- Show: 10/20/50/100/500 rows per table (default 20)

Applies uniformly to By Repo, By Workplan, and Top Tasks tables.
"Most Recent" derives last_event_at per group from the fetched events.
Truncated tables show a "Showing M of N" count below.

Completes CUST-WP-0030 T07–T09.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

workplans/CUST-WP-0030-dashboard-entity-list-ux.md

@@ -4,7 +4,7 @@ type: workplan
 title: "Dashboard Entity List UX"
 domain: custodian
 repo: the-custodian
-status: active
+status: done
 owner: custodian
 topic_slug: custodian
 created: "2026-03-29"