agent: code-atomiser-fix — test_llm_model respects caller GPU preference (Race-8)

Add an Option<bool> use_gpu parameter to test_llm_model with the same
default-true semantics as load_llm_model. Hard-coding true triggered an
engine tear-down/rebuild when a parallel load_llm_model(use_gpu=false)
was in flight (LlmEngine::load_model triples on id+path+use_gpu) and
silently flipped the user's GPU mode underneath the test.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/storage/src/file_storage.rs

@@ -21,8 +21,16 @@ pub fn crashes_dir() -> PathBuf {
     lumotia_core::paths::app_paths().crashes_dir()
 }
 
-/// Directory for the rolling Rust log file (lumotia.log + rotated lumotia.log.1, etc).
-/// Subscribers configured in src-tauri/src/lib.rs at startup.
+/// Directory for the rolling Rust log file.
+///
+/// The base filename is `lumotia.log`; daily rotation produces dated
+/// siblings (e.g. `lumotia.log.2026-05-12`). The appender keeps the
+/// 7 most-recent days and prunes older files on rotation.
+///
+/// Subscriber and rotation policy are configured by `init_tracing` in
+/// `src-tauri/src/lib.rs` at startup; the diagnostic-report bundler in
+/// `src-tauri/src/commands/diagnostics.rs` attaches the live file from
+/// this directory to user-submitted crash reports.
 pub fn logs_dir() -> PathBuf {
     lumotia_core::paths::app_paths().logs_dir()
 }