feat: add sqlite-backed auth and library services

Bootstrap SQLite on server startup with embedded migrations and development seed data. Replace placeholder auth and library responses with database-backed services, bearer sessions, and repository-driven API handlers.

migrations/0001_initial.sql

@@ -7,6 +7,13 @@ CREATE TABLE IF NOT EXISTS users (
   last_login_at TEXT
 );
 
+CREATE TABLE IF NOT EXISTS sessions (
+  token TEXT PRIMARY KEY,
+  user_id TEXT NOT NULL,
+  created_at TEXT NOT NULL,
+  expires_at TEXT NOT NULL
+);
+
 CREATE TABLE IF NOT EXISTS library_roots (
   id TEXT PRIMARY KEY,
   path TEXT NOT NULL UNIQUE,
@@ -72,3 +79,9 @@ CREATE TABLE IF NOT EXISTS favorites (
   created_at TEXT NOT NULL,
   PRIMARY KEY (user_id, entity_id, entity_type)
 );
+
+CREATE INDEX IF NOT EXISTS idx_users_username ON users(username);
+CREATE INDEX IF NOT EXISTS idx_sessions_user_id ON sessions(user_id);
+CREATE INDEX IF NOT EXISTS idx_albums_artist_id ON albums(artist_id);
+CREATE INDEX IF NOT EXISTS idx_tracks_album_id ON tracks(album_id);
+CREATE INDEX IF NOT EXISTS idx_tracks_artist_id ON tracks(artist_id);