feat: add show command with short-index cache

Persist last displayed tweet lists and allow opening a tweet by index.

- Add twitter_cli/cache.py: stores a short-index cache (~/.twitter-cli/last_results.json) with a 1h TTL and helpers to resolve index->tweet-id and cache size.
- Update twitter_cli/cli.py: save list results to cache, display a hint, and add `twitter show <N>` command which fetches a tweet by cached index and prints detail/replies (supports --full-text, --json, structured output, and max replies).
- Update README.md and SKILL.md to document the new `show` usage.
- Add .idea/ to .gitignore and bump package version in uv.lock to 0.8.0.

This change makes it easy to open items from the last feed/search without copying IDs.

twitter_cli/cache.py

@@ -0,0 +1,62 @@
+"""Short-index cache: persist the last displayed tweet list for quick `show` access."""
+
+from __future__ import annotations
+
+import json
+import logging
+import time
+from pathlib import Path
+from typing import List, Optional
+
+from .models import Tweet
+
+logger = logging.getLogger(__name__)
+
+_CACHE_DIR = Path.home() / ".twitter-cli"
+_CACHE_FILE = _CACHE_DIR / "last_results.json"
+_TTL = 3600  # seconds
+
+
+def save_tweet_cache(tweets: List[Tweet]) -> None:
+    """Persist tweet list so indices can be resolved by `show`."""
+    try:
+        _CACHE_DIR.mkdir(parents=True, exist_ok=True)
+        entries = [
+            {"index": i + 1, "id": t.id, "author": t.author.screen_name, "text": t.text[:80]}
+            for i, t in enumerate(tweets)
+            if t.id
+        ]
+        payload = {"created_at": time.time(), "tweets": entries}
+        _CACHE_FILE.write_text(json.dumps(payload, ensure_ascii=False, indent=2), encoding="utf-8")
+    except OSError as exc:
+        logger.debug("Failed to write tweet cache: %s", exc)
+
+
+def _load_cache() -> Optional[List[dict]]:
+    """Load and validate the cache file; return tweet entries or None if stale/missing."""
+    try:
+        if not _CACHE_FILE.exists():
+            return None
+        payload = json.loads(_CACHE_FILE.read_text(encoding="utf-8"))
+        if time.time() - payload.get("created_at", 0) > _TTL:
+            return None
+        return payload.get("tweets", [])
+    except (OSError, json.JSONDecodeError):
+        return None
+
+
+def get_tweet_id_by_index(index: int) -> Optional[str]:
+    """Return tweet ID at *index* (1-based), or None if not found."""
+    entries = _load_cache()
+    if entries is None:
+        return None
+    for entry in entries:
+        if entry.get("index") == index:
+            return str(entry["id"])
+    return None
+
+
+def get_cache_size() -> int:
+    """Return number of tweets in the current cache (0 if unavailable)."""
+    entries = _load_cache()
+    return len(entries) if entries is not None else 0