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>

Cargo.lock

@@ -932,9 +932,11 @@ dependencies = [
  "tokio",
  "tracing",
  "uuid",
+ "zclaw-hands",
  "zclaw-kernel",
  "zclaw-memory",
  "zclaw-runtime",
+ "zclaw-skills",
  "zclaw-types",
 ]
 
@@ -6820,6 +6822,7 @@ version = "0.1.0"
 dependencies = [
  "async-trait",
  "chrono",
+ "reqwest 0.12.28",
  "serde",
  "serde_json",
  "thiserror 2.0.18",
@@ -6851,6 +6854,7 @@ dependencies = [
  "zclaw-memory",
  "zclaw-protocols",
  "zclaw-runtime",
+ "zclaw-skills",
  "zclaw-types",
  "zip",
 ]