- 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
Backend: include all slog attrs in WS payload with sensitive key redaction,
add 100-entry ring buffer for replay on subscribe, support per-client level
selection via logs.tail { level: "debug" }.
Frontend: move log state to Zustand store so tailing persists across page
navigation, add level selector, client-side level filter, text search, and
inline attr rendering.