zmedium: auto re-auth detection and CF block retry-with-backoff

- Detect external re-auth via cookie cache mtime and reset session CF
  counter on next call (no MCP server restart needed).
- Retry transient Cloudflare blocks up to 3 times with random 1-4s
  backoff before surfacing the user-visible "blocked" guidance.
  classifyError stays pure; counter / mtime side effects move to the
  retry orchestrator and only commit after every attempt fails.
- Add tests for the re-auth reset path and a sleep seam for fast tests.
- Ignore local gem Output/ artifacts.

Author: zhgchgli0718

.gitignore

@@ -7,3 +7,4 @@ coverage/
 .vscode/
 .idea/
 *.tsbuildinfo
+Output/

dist/zmedium.d.ts

@@ -8,6 +8,10 @@ export interface RunResult {
     stdout: string;
     warnings: string;
 }
+export declare function _setSleepImplForTests(impl: (ms: number) => Promise<void>): void;
+export declare function _resetSleepImplForTests(): void;
+export declare function _maybeResetForReAuth(): Promise<boolean>;
 export declare function _peekCloudflareBlockCountForTests(): number;
+export declare function _setCloudflareStateForTests(count: number, mtimeBaseline: number | null): void;
 export declare function _resetCloudflareBlockCountForTests(): void;
 export declare function runZMedium(opts: RunOpts): Promise<RunResult>;