refactor(open-sse): P3 provider registry — split into providers/registry/{id}.js

- 100 registry files: transport + models co-located per provider (Mongoose-style)
- providers/shared.js: shared Claude headers + OS/arch helpers (deduped)
- providers/models/helpers.js: withCodexReviewModels (kept dynamic)
- providers/index.js builds PROVIDERS + PROVIDER_MODELS = old API (content byte-for-byte)
- config/providers.js + providerModels.js → barrel re-export, keep accessors + runtime helpers
- Verified: PROVIDERS/MODELS/OAuth/alias byte-for-byte, golden translator tests pass, 0 new regression

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

open-sse/providers/registry/gemini-cli.js

@@ -0,0 +1,20 @@
+export default {
+  "id": "gemini-cli",
+  "alias": "gc",
+  "transport": {
+    "baseUrl": "https://cloudcode-pa.googleapis.com/v1internal",
+    "format": "gemini-cli",
+    "clientId": "681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com",
+    "clientSecret": "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"
+  },
+  "models": [
+    {
+      "id": "gemini-3-flash-preview",
+      "name": "Gemini 3 Flash Preview"
+    },
+    {
+      "id": "gemini-3-pro-preview",
+      "name": "Gemini 3 Pro Preview"
+    }
+  ]
+};