feat: add SQLite database support

- Add sqlite-simple dependency
- Create Sis.Database module with openDatabase (creates parent dir, enables WAL + FK)
- Add --db-path CLI option (default data/sis.db)
- Format all Haskell sources with fourmolu
- Fix hlint suggestions in Sis.Server

src/Sis/Database.hs

@@ -8,13 +8,17 @@ module Sis.Database (
 ) where
 
 import Database.SQLite.Simple qualified as SQL
+import System.Directory (createDirectoryIfMissing)
+import System.FilePath (takeDirectory)
 
--- | Open (or create) a SQLite database at the given path.
---
--- Enables WAL journal mode for concurrent read performance and
--- enables foreign key enforcement.
+{- | Open (or create) a SQLite database at the given path.
+
+Enables WAL journal mode for concurrent read performance and
+enables foreign key enforcement.
+-}
 openDatabase :: FilePath -> IO SQL.Connection
 openDatabase path = do
+    createDirectoryIfMissing True (takeDirectory path)
     conn <- SQL.open path
     SQL.execute_ conn "PRAGMA journal_mode=WAL"
     SQL.execute_ conn "PRAGMA foreign_keys=ON"