fix(kohaku): quiet kt stderr noise + richer live-execution detail

[Yidhar]

Summary

Two follow-up fixes for the live display when KohakuTerrarium (kt) is the core.

1. Quiet kt stderr plugin noise (d756f5b)

kt-biome plugins (PEV verifier, OpenTelemetry exporter) log benign WARNING-level "plugin disabled / no-op" lines on every agent build:

PEV verifier has no acceptance_criteria; plugin disabled
opentelemetry packages not installed; plugin is no-op

Switchyard captures kt's stderr and surfaces it as a failed turn's error_message + an always-saved diagnostics artifact, so this noise dominated the view. The adapter now passes --log-level error to kt run; real turn outcomes arrive on the stdout JSONL (turn_end), independent of the stderr log level, so no failure signal is lost. fake_kt asserts the adapter always passes --log-level.

2. Richer live-execution detail for kt tool activity (4114914)

kt tool/subagent activity was mapped to a generic, content-less command_execution (every tool rendered as "Execute Command"). It now maps to a tool_call carrying the real tool name (from the kt job_id <tool>_<shortid>), the call arguments (path/content — shown via the card's Show-Input toggle, truncated when long), and the result. The stable job_id is the item id, so a tool's start (running, with args) and its done/error (with the result) merge into one transitioning card.

GUI live-execution card:

• Headline falls back to the latest tool of any kind (not just shell commands), so non-command tool turns no longer read "暂无工具事件".
• Adds a "已调用 N 个工具" count for non-command, non-edit tool calls.
• Shows the latest 5 detail cards (was the first 5, which never scrolled to the newest activity) and notes how many earlier ones are folded.

Verification

cargo fmt --all -- --check, cargo clippy -p switchyard-provider-kohaku -p switchyard-tests --all-targets -- -D warnings (on Rust 1.96, matching CI), cargo test -p switchyard-provider-kohaku (14) + --test kohaku_integration (4), and the frontend npm run build all pass.

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