Flowntier v0.4.9 — list_plugins in-process (no sidecar, no kill script)

What changed in v0.4.9

The chairman was right — v0.4.8's error hint told users to run scripts\kill_flowntier.cmd every time they opened Settings. That was bad UX.

Root cause: list_plugins and invoke_plugin in lib.rs were proxying through the sidecar binary via pipe_request('GET', '/api/plugins', None). The sidecar doesn't have a /api/plugins handler (the plugin system is a skeleton with no real plugins). The sidecar returns 404 'no handler registered for path /api/plugins', which the frontend displayed as 'Failed to fetch plugins' with the kill-script hint.

Fix (BUG-FRONTEND-RT-13):

• list_plugins now returns Ok(serde_json::json!([])) directly from the Rust shell — no sidecar roundtrip needed.
• invoke_plugin returns a graceful 'Plugin not registered' error (the plugin system is a v0.5 feature).
• The error hint no longer mentions kill_flowntier.cmd. zh-CN: '提示: 这通常意味着后端没有 /api/plugins 接口。在 v0.4.9+ 插件系统由 Rust 进程直接处理，不再需要 sidecar。如果 v0.4.9+ 仍出现此错误，请上报 bug。' en-US mirrors the same message.

The plugin panel in v0.4.9 will now show 'No plugins available' (empty list) instead of the error message — correct UX since the plugin system is a v0.5 feature.

The user is no longer asked to run a helper script.