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/handlers/ttsProviders/openai.js

@@ -1,11 +1,14 @@
 // OpenAI TTS — model format: "tts-model/voice"
 import { Buffer } from "node:buffer";
+import { PROVIDER_MEDIA } from "../../providers/index.js";
+
+const DEFAULT_TTS_MODEL = PROVIDER_MEDIA["openai"]?.ttsConfig?.defaultModel;
 
 export default {
   async synthesize(text, model, credentials) {
     if (!credentials?.apiKey) throw new Error("No OpenAI API key configured");
 
-    let ttsModel = "gpt-4o-mini-tts";
+    let ttsModel = DEFAULT_TTS_MODEL;
     let voice = "alloy";
     if (model && model.includes("/")) {
       const parts = model.split("/");