feat(proxy): add upstream error and rate-limit tracking support

src/tests/unit/proxy-parity-fixtures.test.ts

@@ -10,6 +10,8 @@ const mockTokenManager = {
   getNextToken: vi.fn(),
   markAsRateLimited: vi.fn(),
   markAsForbidden: vi.fn(),
+  markFromUpstreamError: vi.fn(),
+  recordParityError: vi.fn(),
 };
 const mockGeminiClient = { streamGenerateInternal: vi.fn(), generateInternal: vi.fn() };