Introduced `write_sidecar_log` to prevent temporary `format_args!` values
from dropping early.
- src-tauri/src/core/core.rs:60 — adds `write_sidecar_log`, which temporarily
leaks the message into a `Box<str>`, builds the `Record`, writes it, then
immediately reclaims the boxed string. The `unsafe` block is limited to
`Box::from_raw` needed to undo `Box::leak`.
- src-tauri/src/core/core.rs:794, 802, 806 — all three sidecar events now route
through this helper, reusing the returned string for the in-memory log and
avoiding extra UTF-8 decoding.
fe7eb59f18