feat: add whoami, reply, quote, follow/unfollow commands and --compact mode

- whoami: fetch current authenticated user profile
- reply <id> <text>: standalone reply command
- quote <id> <text>: quote-tweet command
- follow/unfollow <handle>: follow/unfollow users
- --compact/-c: global flag for LLM-friendly minimal JSON output
- client.py: add fetch_me, quote_tweet, follow_user, unfollow_user
- serialization.py: add tweet_to_compact_dict, tweets_to_compact_json
- 7 new tests (82 total, all passing)

twitter_cli/serialization.py

@@ -129,6 +129,36 @@ def tweets_to_json(tweets: Iterable[Tweet]) -> str:
     return json.dumps([tweet_to_dict(tweet) for tweet in tweets], ensure_ascii=False, indent=2)
 
 
+def tweet_to_compact_dict(tweet: Tweet) -> Dict[str, Any]:
+    """Convert a Tweet into a compact dict with minimal fields for LLM consumption."""
+    text = tweet.text.replace("\n", " ").strip()
+    if len(text) > 140:
+        text = text[:137] + "..."
+    # Short time: "Mar 07 05:51" from "Sat Mar 07 05:51:02 +0000 2026"
+    parts = tweet.created_at.split()
+    if len(parts) >= 4:
+        time_str = "%s %s %s" % (parts[1], parts[2], parts[3][:5])
+    else:
+        time_str = tweet.created_at
+    return {
+        "id": tweet.id,
+        "author": "@%s" % tweet.author.screen_name,
+        "text": text,
+        "likes": tweet.metrics.likes,
+        "rts": tweet.metrics.retweets,
+        "time": time_str,
+    }
+
+
+def tweets_to_compact_json(tweets: Iterable[Tweet]) -> str:
+    """Serialize Tweet objects to compact JSON (minimal fields for LLM/pipe usage)."""
+    return json.dumps(
+        [tweet_to_compact_dict(tweet) for tweet in tweets],
+        ensure_ascii=False,
+        indent=2,
+    )
+
+
 def user_profile_to_dict(user: UserProfile) -> Dict[str, Any]:
     """Convert a UserProfile dataclass into a JSON-safe dict."""
     return {