Implements the /metrics route with DateRangePicker bar, 5 KPI StatCards
with sparklines (throughput, latency p99, error rate, success rate,
active routes), per-route DataTable with trend sparklines, and a 2x2
chart grid (AreaChart throughput, LineChart latency with SLA threshold,
BarChart errors, AreaChart volume). Uses AppShell + Sidebar + TopBar
layout with mock data from src/mocks/metrics.ts.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
