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>

tests/unit/antigravity-oauth-client.test.js

@@ -31,8 +31,7 @@ describe("antigravity oauth client (deduped)", () => {
     expect(gc.transport.clientSecret).toBe(GOOGLE.clientSecret);
   });
 
-  // Vitest can't resolve the `@/` alias used inside oauth.js (pre-existing infra gap),
-  // so guard the refactor textually: it must spread the shared client + keep other fields.
+  // Guard: oauth.js must spread shared clients + derive from registry (PROVIDER_OAUTH).
   it("src oauth.js imports shared client + keeps full shape", async () => {
     const { readFileSync } = await import("node:fs");
     const { fileURLToPath } = await import("node:url");
@@ -42,7 +41,9 @@ describe("antigravity oauth client (deduped)", () => {
     expect(src).toContain('import { ANTIGRAVITY_OAUTH_CLIENT, GOOGLE_OAUTH_CLIENT } from "open-sse/providers/shared.js"');
     expect(src).toContain("...ANTIGRAVITY_OAUTH_CLIENT");
     expect(src).toContain("...GOOGLE_OAUTH_CLIENT");
-    expect(src).toContain('authorizeUrl: "https://accounts.google.com/o/oauth2/v2/auth"');
+    // authorizeUrl now lives in registry; oauth.js derives via PROVIDER_OAUTH spread
+    expect(src).toContain('PROVIDER_OAUTH["antigravity"]');
+    expect(src).toContain('PROVIDER_OAUTH["gemini-cli"]');
     expect(src).not.toContain(EXPECTED.clientSecret); // antigravity secret no longer hardcoded here
     expect(src).not.toContain(GOOGLE.clientSecret);   // gemini secret no longer hardcoded here
   });