- Update go.mod and Dockerfile to Go 1.26
- Apply `go fix ./...` stdlib modernizations across 170+ files
- Add `go fix` to post-implementation checklist in CLAUDE.md
- Fix go fix misapplied rewrite in loop_history.go
Add a no-op use_skill tool that generates tool.call/tool.result events
in tracing spans and realtime, making skill activations visible in
observability. The actual skill loading still happens via read_file.
Web UI renders use_skill events with a distinct Zap icon and skill name
instead of the generic wrench icon.