refactor(app): DRY pass — split large files, extract shared utils

S1: delete page.new.js (1724L abandoned) + remove dead getAntigravityProjectId
S2: split large files by natural seams
  - usage.js → usage/{github,google,claude,codex,kiro,minimax,misc,shared}.js
  - media-providers page → components/{Embedding,Tts,Generic,Stt}ExampleCard.js
  - EndpointPageClient → endpointConstants.js + endpointPing.js + components/
  - tokenRefresh.js → tokenRefresh/{dedup,providers}.js
  - ProviderLimits/index.js: 16 pure fn + 9 constants → utils.js
  - oauth/providers.js: 7 pure helpers → providerHelpers.js
S3: shared utils
  - getModelKind(m, fallback) → shared/constants/models.js (replaces 20× m.kind||m.type)
  - getStatusVariant → shared/utils/connectionStatus.js (dedup ConnectionRow/ConnectionsCard)
  - sseChunk → open-sse/utils/sse.js (dedup grok-web/perplexity-web)
  - fetchWithTimeout → usage/shared.js (replace 4× AbortController pattern in google.js)
fix: enableObservability2 field name in requestDetailsRepo
Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/services/tokenRefresh/dedup.js

@@ -0,0 +1,31 @@
+const REFRESH_RESULT_TTL_MS = 10_000;
+const refreshDedupCache = new Map();
+
+export async function dedupRefresh(provider, oldToken, fn, log) {
+  if (!oldToken) return fn();
+  const key = `${provider}:${oldToken}`;
+  const hit = refreshDedupCache.get(key);
+  if (hit) {
+    if (hit.promise) {
+      log?.info?.("TOKEN_REFRESH", `Reusing in-flight refresh for ${provider}`);
+      return hit.promise;
+    }
+    if (hit.expiresAt > Date.now()) {
+      log?.info?.("TOKEN_REFRESH", `Reusing recent refresh result for ${provider}`);
+      return hit.result;
+    }
+    refreshDedupCache.delete(key);
+  }
+  const promise = (async () => {
+    try {
+      const result = await fn();
+      refreshDedupCache.set(key, { result, expiresAt: Date.now() + REFRESH_RESULT_TTL_MS });
+      return result;
+    } catch (err) {
+      refreshDedupCache.delete(key);
+      throw err;
+    }
+  })();
+  refreshDedupCache.set(key, { promise });
+  return promise;
+}