feat(hands): implement 4 new Hands and fix BrowserHand registration

- Add ResearcherHand: DuckDuckGo search, web fetch, report generation
- Add CollectorHand: data collection, aggregation, multiple output formats
- Add ClipHand: video processing (trim, convert, thumbnail, concat)
- Add TwitterHand: Twitter/X automation (tweet, retweet, like, search)
- Fix BrowserHand not registered in Kernel (critical bug)
- Add HandError variant to ZclawError enum
- Update documentation: 9/11 Hands implemented (82%)

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

crates/zclaw-hands/src/hands/mod.rs

@@ -6,15 +6,27 @@
 //! - Speech: Text-to-speech synthesis
 //! - Quiz: Assessment and evaluation
 //! - Browser: Web automation
+//! - Researcher: Deep research and analysis
+//! - Collector: Data collection and aggregation
+//! - Clip: Video processing
+//! - Twitter: Social media automation
 
 mod whiteboard;
 mod slideshow;
 mod speech;
 mod quiz;
 mod browser;
+mod researcher;
+mod collector;
+mod clip;
+mod twitter;
 
 pub use whiteboard::*;
 pub use slideshow::*;
 pub use speech::*;
 pub use quiz::*;
 pub use browser::*;
+pub use researcher::*;
+pub use collector::*;
+pub use clip::*;
+pub use twitter::*;