Fix critical integration issues for end-to-end functionality

- Rewrite SidecarManager as singleton with OnceLock, reusing one Python
  process across all commands instead of spawning per call
- Separate stdin/stdout ownership with dedicated BufReader to prevent
  data corruption between wait_for_ready and send_and_receive
- Add ensure_running() for auto-start on first command
- Fix asset protocol URL: use convertFileSrc() instead of manual
  encodeURIComponent which broke file paths with slashes
- Add +layout.svelte with global dark theme, CSS reset, and custom
  scrollbar styling to prevent white flash on startup
- Register AppState with Tauri .manage(), initialize SQLite database
  on app startup at ~/.voicetonotes/voice_to_notes.db
- Wire project commands (create/get/list) to real database queries
  instead of placeholder stubs

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

src-tauri/src/lib.rs

@@ -10,12 +10,16 @@ use commands::project::{create_project, get_project, list_projects};
 use commands::settings::{load_settings, save_settings};
 use commands::system::{get_data_dir, llama_list_models, llama_start, llama_status, llama_stop};
 use commands::transcribe::{run_pipeline, transcribe_file};
+use state::AppState;
 
 #[cfg_attr(mobile, tauri::mobile_entry_point)]
 pub fn run() {
+    let app_state = AppState::new().expect("Failed to initialize app state");
+
     tauri::Builder::default()
         .plugin(tauri_plugin_opener::init())
         .plugin(tauri_plugin_dialog::init())
+        .manage(app_state)
         .invoke_handler(tauri::generate_handler![
             create_project,
             get_project,