feat(bluesky): add Bluesky/AT Protocol as social source

Free, no-auth-required search via public.api.bsky.app.
Always-on like HN and Polymarket (no API key needed).

- New scripts/lib/bluesky.py: search + parse via AT Protocol
- BlueskyItem schema, normalization, scoring, deduplication
- Wired into orchestrator ThreadPoolExecutor with timeout config
- Rendering in compact, full, and JSON output modes
- 14 unit tests covering parsing, dates, relevance, edge cases
- --search=bluesky / --search=bsky for bluesky-only mode

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/lib/dedupe.py

@@ -226,6 +226,14 @@ def dedupe_hackernews(
     return dedupe_items(items, threshold)
 
 
+def dedupe_bluesky(
+    items: List[schema.BlueskyItem],
+    threshold: float = 0.7,
+) -> List[schema.BlueskyItem]:
+    """Dedupe Bluesky items."""
+    return dedupe_items(items, threshold)
+
+
 def dedupe_polymarket(
     items: List[schema.PolymarketItem],
     threshold: float = 0.7,