M-002 spike slices

Throwaway validation surfaces for SPIKE-002 (frontend state) and SPIKE-003 (charting). Removed when production dashboards land in SDD-004.

• /spike/agent-log — TanStack Query polling at 5 s (SPIKE-002).
• /spike/filters — nuqs URL-state demo (SPIKE-002).
• /spike/charts — token-themed chart with per-tenant toggle (SPIKE-003).