feat: anti-detection hardening, transaction cache, article parsing, structured write output

Anti-detection:
- Add 6 sec-ch-ua-* Client Hints headers (arch, bitness, full-version, etc.)
- POST requests now send Referer: x.com/compose/post + Priority: u=1, i
- follow/unfollow REST adds include_profile_interstitial_type param

Performance:
- Transaction ID cache with 1h TTL (~/.twitter-cli/transaction_cache.json)
- resolve_user_id: auto-detect screen_name vs numeric user_id

Features:
- Twitter Article parsing: extract long-form content as Markdown
- Write operations emit structured JSON/YAML when piped or OUTPUT env set
  ActionResult: {success, action, id, url, ...}

84 tests passing

tests/conftest.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import json
+import os
 from pathlib import Path
 from typing import Any
 
@@ -8,6 +9,8 @@ import pytest
 
 from twitter_cli.models import Author, Metrics, Tweet
 
+os.environ.setdefault("OUTPUT", "rich")
+
 
 @pytest.fixture()
 def tweet_factory():