perf: bound SWR cache, clean stale storage, cap annotations

Add LRU cache provider (200 entries) to prevent unbounded SWR memory
growth. Clean up stale PKCE localStorage keys on app init. Cap chart
annotations to 20 visible reference lines with overflow indicator.

components/SWRProvider.tsx

@@ -0,0 +1,12 @@
+'use client'
+
+import { SWRConfig } from 'swr'
+import { boundedCacheProvider } from '@/lib/swr/cache-provider'
+
+export default function SWRProvider({ children }: { children: React.ReactNode }) {
+  return (
+    <SWRConfig value={{ provider: boundedCacheProvider }}>
+      {children}
+    </SWRConfig>
+  )
+}