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/imageProviders/codex.js

@@ -1,8 +1,9 @@
 // Codex (ChatGPT Plus/Pro) image generation via Responses API + SSE
 import { randomUUID } from "node:crypto";
 import { nowSec } from "./_base.js";
+import { PROVIDERS } from "../../config/providers.js";
 
-const CODEX_RESPONSES_URL = "https://chatgpt.com/backend-api/codex/responses";
+const CODEX_RESPONSES_URL = PROVIDERS["codex"].baseUrl;
 const CODEX_USER_AGENT = "codex_cli_rs/0.136.0";
 const CODEX_VERSION = "0.136.0";
 const CODEX_ORIGINATOR = "codex_cli_rs";