feat(providers): expose antigravity preview aliases and gemini cli onboarding

Centralize Antigravity public model definitions and use the
client-visible preview aliases in provider discovery, model catalog
responses, and default alias seeding.

Add Gemini CLI managed-project onboarding with retries when
loadCodeAssist does not return a project, and update Gemini CLI header
fingerprints to match newer native clients.

Improve non-stream handling by converting NDJSON event payloads into
SSE-compatible parsing for stream=false requests, add PUT support for
the settings API, expand Gemini schema cleanup for local refs and
unsupported keys, and include Anthropic beta headers for API-key
requests.

tests/unit/settings-api.test.ts

@@ -1,6 +1,7 @@
 import { describe, test } from "node:test";
 import assert from "node:assert/strict";
 import { getSettings, updateSettings } from "../../src/lib/db/settings.ts";
+const settingsRoute = await import("../../src/app/api/settings/route.ts");
 
 describe("Settings API - debugMode and hiddenSidebarItems", () => {
   describe("debugMode", () => {
@@ -77,5 +78,19 @@ describe("Settings API - debugMode and hiddenSidebarItems", () => {
         "antigravitySignatureCacheMode should be updated"
       );
     });
+
+    test("PUT /api/settings reuses the PATCH update flow", async () => {
+      const response = await settingsRoute.PUT(
+        new Request("http://localhost/api/settings", {
+          method: "PUT",
+          headers: { "Content-Type": "application/json" },
+          body: JSON.stringify({ antigravitySignatureCacheMode: "bypass" }),
+        })
+      );
+      const body = await response.json();
+
+      assert.equal(response.status, 200);
+      assert.equal(body.antigravitySignatureCacheMode, "bypass");
+    });
   });
 });