Fix IPC stdout corruption, dark window background, overlay timing

- Redirect sys.stdout to stderr in Python sidecar so library print()
  calls don't corrupt the JSON-line IPC stream
- Save real stdout fd for exclusive IPC use via init_ipc()
- Skip non-JSON lines in Rust reader instead of failing with parse error
- Set Tauri window background color to match dark theme (#0a0a23)
- Add inline dark background on html/body to prevent white flash
- Use Svelte tick() to ensure progress overlay renders before invoke
- Improve ProgressOverlay with spinner, better styling, z-index 9999

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -4,6 +4,9 @@ pub mod llama;
 pub mod sidecar;
 pub mod state;
 
+use tauri::window::Color;
+use tauri::Manager;
+
 use commands::ai::{ai_chat, ai_configure, ai_list_providers};
 use commands::export::export_transcript;
 use commands::project::{create_project, get_project, list_projects};
@@ -20,6 +23,13 @@ pub fn run() {
         .plugin(tauri_plugin_opener::init())
         .plugin(tauri_plugin_dialog::init())
         .manage(app_state)
+        .setup(|app| {
+            // Set the webview background to match the app's dark theme
+            if let Some(window) = app.get_webview_window("main") {
+                let _ = window.set_background_color(Some(Color(10, 10, 35, 255)));
+            }
+            Ok(())
+        })
         .invoke_handler(tauri::generate_handler![
             create_project,
             get_project,