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>

src/lib/oauth/providers.js

@@ -200,8 +200,8 @@ const PROVIDERS = {
   codex: {
     config: CODEX_CONFIG,
     flowType: "authorization_code_pkce",
-    fixedPort: 1455,
-    callbackPath: "/auth/callback",
+    fixedPort: CODEX_CONFIG.fixedPort,
+    callbackPath: CODEX_CONFIG.callbackPath,
     buildAuthUrl: (config, redirectUri, state, codeChallenge) => {
       const params = {
         response_type: "code",