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>

src/app/(dashboard)/dashboard/providers/components/ModelsCard.js

@@ -3,7 +3,7 @@
 import { useState, useCallback, useEffect } from "react";
 import PropTypes from "prop-types";
 import { Card, Button, Modal } from "@/shared/components";
-import { getModelsByProviderId } from "@/shared/constants/models";
+import { getModelsByProviderId, getModelKind } from "@/shared/constants/models";
 import { getProviderAlias } from "@/shared/constants/providers";
 import { useCopyToClipboard } from "@/shared/hooks/useCopyToClipboard";
 
@@ -206,14 +206,14 @@ export default function ModelsCard({ providerId, kindFilter, providerAliasOverri
   const builtInModels = kindFilter
     ? allBuiltIn.filter((m) => {
         if (m.kinds) return m.kinds.includes(kindFilter);
-        return (m.kind || m.type || "llm") === kindFilter;
+        return getModelKind(m, "llm") === kindFilter;
       })
     : allBuiltIn;
 
   // Custom models for this provider + kind, dedupe vs built-in
   const myCustomModels = customModels.filter(
     (m) => m.providerAlias === providerAlias
-      && (m.kind || m.type || "llm") === effectiveType
+      && getModelKind(m, "llm") === effectiveType
       && !builtInModels.some((b) => b.id === m.id)
   );