agent: lumotia-rebrand — tracing filter targets

Phase 4 of the rebrand cascade. Updates the default RUST_LOG filter
in src-tauri/src/lib.rs and all 'target: "magnotia_startup"' string
literals across src-tauri/src/lib.rs and src-tauri/src/commands/models.rs.

Default filter (before):
  warn,magnotia=info,lumotia_lib=info,lumotia_audio=info,
  magnotia_startup=info,lumotia_hotkey=info,lumotia_ai_formatting=info

Default filter (after):
  warn,lumotia=info,lumotia_lib=info,lumotia_core=info,
  lumotia_audio=info,lumotia_hotkey=info,lumotia_ai_formatting=info,
  lumotia_llm=info,lumotia_storage=info,lumotia_transcription=info,
  lumotia_startup=info

magnotia_startup was a logical tracing target (not a crate); renamed
to lumotia_startup for consistency. magnotia_lib was already renamed
to lumotia_lib in Phase 2. Added per-crate filter entries for parity
across the workspace.

cargo build --workspace passes. cargo test --workspace: 330 pass, 0 fail.

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

src-tauri/src/commands/models.rs

@@ -208,11 +208,11 @@ pub fn prewarm_default_model(whisper_engine: Arc<LocalEngine>) {
                 let options = TranscriptionOptions::default();
                 match whisper_engine.transcribe_sync(&silence, &options) {
                     Ok(_) => tracing::info!(
-                        target: "magnotia_startup",
+                        target: "lumotia_startup",
                         "Whisper warm-up inference complete"
                     ),
                     Err(e) => tracing::warn!(
-                        target: "magnotia_startup",
+                        target: "lumotia_startup",
                         error = %e,
                         "Whisper warm-up inference failed"
                     ),
@@ -223,16 +223,16 @@ pub fn prewarm_default_model(whisper_engine: Arc<LocalEngine>) {
 
         match result {
             Ok(Ok(())) => tracing::info!(
-                target: "magnotia_startup",
+                target: "lumotia_startup",
                 "Whisper model pre-warmed successfully"
             ),
             Ok(Err(e)) => tracing::warn!(
-                target: "magnotia_startup",
+                target: "lumotia_startup",
                 error = %e,
                 "Whisper pre-warm failed"
             ),
             Err(e) => tracing::error!(
-                target: "magnotia_startup",
+                target: "lumotia_startup",
                 error = %e,
                 "Whisper pre-warm task panicked"
             ),