refactor(open-sse): merge beta-url case + single-source refresh URLs (D)

buildUrl: fold kimi-coding into the shared ?beta=true case. refreshCline/
refreshKimiCoding now read URL (and kimi-coding clientId) from PROVIDERS instead
of hardcoded strings. Extend verify-oauth-urls with refresh/clientId snapshot;
URLs byte-for-byte equal, golden + gate clean.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/__baseline__/verify-oauth-urls.mjs

@@ -27,6 +27,18 @@ const resolved = {
     iflow: PROVIDERS.iflow?.authUrl,
     kiro: PROVIDERS.kiro?.authUrl,
   },
+  refreshUrls: {
+    cline: PROVIDERS.cline?.refreshUrl,
+    "kimi-coding": PROVIDERS["kimi-coding"]?.refreshUrl,
+    xai: PROVIDERS.xai?.refreshUrl,
+  },
+  clientIds: {
+    claude: PROVIDERS.claude?.clientId,
+    codex: PROVIDERS.codex?.clientId,
+    qwen: PROVIDERS.qwen?.clientId,
+    iflow: PROVIDERS.iflow?.clientId,
+    "kimi-coding": PROVIDERS["kimi-coding"]?.clientId,
+  },
 };
 const current = JSON.parse(JSON.stringify(resolved));