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-types/src/error.rs

@@ -55,6 +55,9 @@ pub enum ZclawError {
 
     #[error("Security error: {0}")]
     SecurityError(String),
+
+    #[error("Hand error: {0}")]
+    HandError(String),
 }
 
 /// Result type alias for ZCLAW operations