refactor(open-sse): registry consolidation + DRY media/oauth/adhoc cleanup

- Single-source registry: oauth clientId/tokenUrl, usage URLs, image/embed
  configs, search defaultModel, codex fixedPort, google token url derive.
- Remove 29 unused OmniRoute providers (registry 100→71); media intact.
- De-adhoc: codex literals → registry format/oauth flags; reasoningInject,
  image/embed openrouter headers + xai bodyFields config-driven.
- Add REGISTRY_TEMPLATE.js + expand PROVIDER_DEFAULTS/schema JSDoc.
- Baselines updated; PROVIDERS 62 + alias 90 byte-for-byte, golden snapshots.

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

open-sse/translator/helpers/imageHelper.js

@@ -3,6 +3,15 @@ export function encodeDataUri(mimeType, base64) {
   return `data:${mimeType};base64,${base64}`;
 }
 
+// Parse a base64 data URI → { mimeType, base64 }, or null if not a data URI.
+// [\s\S] tolerates newlines inside the base64 payload.
+const DATA_URI_RE = /^data:([^;]+);base64,([\s\S]+)$/;
+export function parseDataUri(url) {
+  if (typeof url !== "string") return null;
+  const m = url.match(DATA_URI_RE);
+  return m ? { mimeType: m[1], base64: m[2] } : null;
+}
+
 /**
  * Fetch a remote image URL and return it as a base64 data URI.
  * Used when upstream providers (Codex, etc.) require inline base64 images