fix: P0 Windows Edge path, add time localization, show --output, cleanup tech debt

- Fix auth.py subprocess script Windows Edge cookie path inconsistency
- Add timeutil.py for UTC→local time and relative time conversion
- Integrate time localization into formatter.py and serialization.py
- Add --output/-o option to show command for saving tweet detail as JSON
- Remove constants.py legacy aliases (USER_AGENT, SEC_CH_UA)
- Remove client.py backward-compat delegation methods and re-exports
- Update test imports to use parser module directly

twitter_cli/serialization.py

@@ -6,6 +6,7 @@ import json
 from typing import Any, Dict, Iterable, List, Optional
 
 from .models import Author, Metrics, Tweet, TweetMedia, UserProfile
+from .timeutil import format_local_time
 
 
 def tweet_to_dict(tweet: Tweet) -> Dict[str, Any]:
@@ -29,6 +30,7 @@ def tweet_to_dict(tweet: Tweet) -> Dict[str, Any]:
             "bookmarks": tweet.metrics.bookmarks,
         },
         "createdAt": tweet.created_at,
+        "createdAtLocal": format_local_time(tweet.created_at),
         "media": [
             {
                 "type": media.type,