fix: rate-probabilities → European region + stronger browser headers

- preferredRegion: fra1/lhr1/cdg1 to bypass US cloud IP blocks on rateprobability.com
- Better sec-* headers to pass bot detection (same-origin cors mode)
- cache: no-store on fetch to avoid stale null caching
- Log CB count on each invocation for diagnostics

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

lib/rateprobability.ts

@@ -100,11 +100,19 @@ async function fetchCBPath(ccy: Currency, slug: string): Promise<CBRatePath | nu
   try {
     const res = await fetch(`https://rateprobability.com/api/${slug}/latest`, {
       headers: {
-        "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 Chrome/124.0.0.0 Safari/537.36",
-        "Referer":    `https://rateprobability.com/${slug}`,
-        "Accept":     "application/json, */*",
+        "User-Agent":      "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/125.0.0.0 Safari/537.36",
+        "Referer":         `https://rateprobability.com/${slug}`,
+        "Origin":          "https://rateprobability.com",
+        "Accept":          "application/json, text/plain, */*",
+        "Accept-Language": "en-US,en;q=0.9",
+        "Accept-Encoding": "gzip, deflate, br",
+        "sec-ch-ua":       '"Chromium";v="125", "Not.A/Brand";v="24"',
+        "sec-ch-ua-mobile":"?0",
+        "sec-fetch-dest":  "empty",
+        "sec-fetch-mode":  "cors",
+        "sec-fetch-site":  "same-origin",
       },
-      next: { revalidate: 3600 },
+      cache: "no-store",
     });
     if (!res.ok) return null;
     const body  = await res.json() as Record<string, unknown>;