feat(core): implement secure MVP core with dictionary search, auth, and CRUD

app/database.py

@@ -0,0 +1,77 @@
+import sqlite3
+import contextlib
+from typing import Generator
+from app import config
+
+def get_db_connection() -> sqlite3.Connection:
+    conn = sqlite3.connect(
+        config.DB_PATH,
+        timeout=15.0
+    )
+    conn.row_factory = sqlite3.Row
+    conn.execute("PRAGMA journal_mode=WAL;")
+    conn.execute("PRAGMA synchronous=NORMAL;")
+    conn.execute("PRAGMA foreign_keys=ON;")
+    return conn
+
+@contextlib.contextmanager
+def get_db() -> Generator[sqlite3.Connection, None, None]:
+    conn = get_db_connection()
+    try:
+        yield conn
+        conn.commit()
+    except Exception:
+        conn.rollback()
+        raise
+    finally:
+        conn.close()
+
+def init_db():
+    config.DB_PATH.parent.mkdir(parents=True, exist_ok=True)
+    with get_db() as conn:
+        conn.executescript("""
+        CREATE TABLE IF NOT EXISTS users (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            username TEXT UNIQUE NOT NULL COLLATE NOCASE,
+            password_hash TEXT NOT NULL,
+            salt TEXT NOT NULL,
+            created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+        );
+
+        CREATE TABLE IF NOT EXISTS sessions (
+            token TEXT PRIMARY KEY,
+            user_id INTEGER NOT NULL,
+            created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+            expires_at TIMESTAMP NOT NULL,
+            user_agent TEXT,
+            ip TEXT,
+            FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
+        );
+
+        CREATE TABLE IF NOT EXISTS vocabulary_cards (
+            id INTEGER PRIMARY KEY AUTOINCREMENT,
+            user_id INTEGER NOT NULL,
+            term TEXT NOT NULL,
+            translation TEXT NOT NULL,
+            context_sentence TEXT,
+            phonetic TEXT,
+            audio_url TEXT,
+            part_of_speech TEXT,
+            definition_en TEXT,
+            tags TEXT,
+            notes TEXT,
+            created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+            updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+            FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
+        );
+
+        CREATE INDEX IF NOT EXISTS idx_vocab_user ON vocabulary_cards(user_id);
+        CREATE INDEX IF NOT EXISTS idx_vocab_term ON vocabulary_cards(term);
+        CREATE INDEX IF NOT EXISTS idx_vocab_created ON vocabulary_cards(created_at DESC);
+
+        CREATE TABLE IF NOT EXISTS dictionary_cache (
+            query TEXT PRIMARY KEY COLLATE NOCASE,
+            response_json TEXT NOT NULL,
+            cached_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+        );
+        """)