refactor: establish database migration foundation

backend/database/connection.py

@@ -0,0 +1,33 @@
+from __future__ import annotations
+
+import sqlite3
+from dataclasses import dataclass
+from pathlib import Path
+
+
+class ManagedConnection(sqlite3.Connection):
+    """Commit or roll back, then release the SQLite handle on context exit."""
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        try:
+            return super().__exit__(exc_type, exc_value, traceback)
+        finally:
+            self.close()
+
+
+@dataclass(frozen=True)
+class SQLiteConnectionFactory:
+    path: Path
+    timeout_seconds: float = 20
+
+    def connect(self) -> sqlite3.Connection:
+        connection = sqlite3.connect(
+            self.path,
+            timeout=self.timeout_seconds,
+            factory=ManagedConnection,
+        )
+        connection.row_factory = sqlite3.Row
+        connection.execute("PRAGMA journal_mode=WAL")
+        connection.execute("PRAGMA foreign_keys=ON")
+        connection.execute("PRAGMA busy_timeout=20000")
+        return connection