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/providers/registry/llm7.js

@@ -1,21 +0,0 @@
-export default {
-  "id": "llm7",
-  "alias": "llm7",
-  "transport": {
-    "baseUrl": "https://api.llm7.io/v1/chat/completions"
-  },
-  "models": [
-    {
-      "id": "gpt-4o-mini",
-      "name": "GPT-4o Mini"
-    },
-    {
-      "id": "gpt-4.1-mini",
-      "name": "GPT-4.1 Mini"
-    },
-    {
-      "id": "gemini-1.5-flash",
-      "name": "Gemini 1.5 Flash"
-    }
-  ]
-};