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/state.rs

@@ -3,17 +3,28 @@ use std::sync::Mutex;
 
 use rusqlite::Connection;
 
+use crate::db;
+use crate::llama::LlamaManager;
+
 /// Shared application state managed by Tauri.
 pub struct AppState {
-    pub db: Mutex<Option<Connection>>,
+    pub db: Mutex<Connection>,
     pub data_dir: PathBuf,
 }
 
 impl AppState {
-    pub fn new(data_dir: PathBuf) -> Self {
-        Self {
-            db: Mutex::new(None),
+    pub fn new() -> Result<Self, String> {
+        let data_dir = LlamaManager::data_dir();
+        std::fs::create_dir_all(&data_dir)
+            .map_err(|e| format!("Cannot create data dir: {e}"))?;
+
+        let db_path = data_dir.join("voice_to_notes.db");
+        let conn = db::open_database(&db_path)
+            .map_err(|e| format!("Cannot open database: {e}"))?;
+
+        Ok(Self {
+            db: Mutex::new(conn),
             data_dir,
-        }
+        })
     }
 }