feat(auth): update constants to match CLIProxyAPI (50min buffer, 2 endpoints)

- Changed ANTIGRAVITY_TOKEN_REFRESH_BUFFER_MS from 60,000ms (1min) to 3,000,000ms (50min)
- Removed autopush endpoint from ANTIGRAVITY_ENDPOINT_FALLBACKS (now 2 endpoints: daily → prod)
- Added comprehensive test suite with 6 tests covering all updated constants
- Updated comments to reflect CLIProxyAPI parity

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/auth/antigravity/constants.test.ts

@@ -0,0 +1,62 @@
+import { describe, it, expect } from "bun:test"
+import {
+  ANTIGRAVITY_TOKEN_REFRESH_BUFFER_MS,
+  ANTIGRAVITY_ENDPOINT_FALLBACKS,
+  ANTIGRAVITY_CALLBACK_PORT,
+} from "./constants"
+
+describe("Antigravity Constants", () => {
+  describe("ANTIGRAVITY_TOKEN_REFRESH_BUFFER_MS", () => {
+    it("should be 50 minutes (3,000,000ms) to match CLIProxyAPI", () => {
+      // #given
+      const FIFTY_MINUTES_MS = 50 * 60 * 1000 // 3,000,000
+
+      // #when
+      const actual = ANTIGRAVITY_TOKEN_REFRESH_BUFFER_MS
+
+      // #then
+      expect(actual).toBe(FIFTY_MINUTES_MS)
+    })
+  })
+
+  describe("ANTIGRAVITY_ENDPOINT_FALLBACKS", () => {
+    it("should have exactly 2 endpoints (daily → prod)", () => {
+      // #given
+      const expectedCount = 2
+
+      // #when
+      const actual = ANTIGRAVITY_ENDPOINT_FALLBACKS
+
+      // #then
+      expect(actual).toHaveLength(expectedCount)
+    })
+
+    it("should have daily endpoint first", () => {
+      // #then
+      expect(ANTIGRAVITY_ENDPOINT_FALLBACKS[0]).toBe(
+        "https://daily-cloudcode-pa.sandbox.googleapis.com"
+      )
+    })
+
+    it("should have prod endpoint second", () => {
+      // #then
+      expect(ANTIGRAVITY_ENDPOINT_FALLBACKS[1]).toBe(
+        "https://cloudcode-pa.googleapis.com"
+      )
+    })
+
+    it("should NOT include autopush endpoint", () => {
+      // #then
+      const endpointsJoined = ANTIGRAVITY_ENDPOINT_FALLBACKS.join(",")
+      const hasAutopush = endpointsJoined.includes("autopush-cloudcode-pa")
+      expect(hasAutopush).toBe(false)
+    })
+  })
+
+  describe("ANTIGRAVITY_CALLBACK_PORT", () => {
+    it("should be 51121 to match CLIProxyAPI", () => {
+      // #then
+      expect(ANTIGRAVITY_CALLBACK_PORT).toBe(51121)
+    })
+  })
+})