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/commands/project.rs

@@ -1,27 +1,23 @@
+use tauri::State;
+
 use crate::db::models::Project;
+use crate::db::queries;
+use crate::state::AppState;
 
 #[tauri::command]
-pub fn create_project(name: String) -> Result<Project, String> {
-    // TODO: Use actual database connection from app state
-    Ok(Project {
-        id: uuid::Uuid::new_v4().to_string(),
-        name,
-        created_at: chrono::Utc::now().to_rfc3339(),
-        updated_at: chrono::Utc::now().to_rfc3339(),
-        settings: None,
-        status: "active".to_string(),
-    })
+pub fn create_project(name: String, state: State<AppState>) -> Result<Project, String> {
+    let conn = state.db.lock().map_err(|e| e.to_string())?;
+    queries::create_project(&conn, &name).map_err(|e| e.to_string())
 }
 
 #[tauri::command]
-pub fn get_project(id: String) -> Result<Option<Project>, String> {
-    // TODO: Use actual database connection from app state
-    let _ = id;
-    Ok(None)
+pub fn get_project(id: String, state: State<AppState>) -> Result<Option<Project>, String> {
+    let conn = state.db.lock().map_err(|e| e.to_string())?;
+    queries::get_project(&conn, &id).map_err(|e| e.to_string())
 }
 
 #[tauri::command]
-pub fn list_projects() -> Result<Vec<Project>, String> {
-    // TODO: Use actual database connection from app state
-    Ok(vec![])
+pub fn list_projects(state: State<AppState>) -> Result<Vec<Project>, String> {
+    let conn = state.db.lock().map_err(|e| e.to_string())?;
+    queries::list_projects(&conn).map_err(|e| e.to_string())
 }