feat(01-02): add Peewee models, database init, and driver storage

- imptune/db/database.py: deferred SqliteDatabase with WAL + foreign_keys pragmas and init_db()
- imptune/db/models.py: full schema (Client, Driver, Printer, Icon) for phases 1-5
- imptune/storage/driver_store.py: SHA256 content-addressed DriverStore with dedup
- tests/test_db.py: 7 TDD tests covering all db and storage behaviors

imptune/storage/__init__.py

@@ -0,0 +1 @@
+# Storage package

imptune/storage/driver_store.py

@@ -0,0 +1,34 @@
+"""Content-addressed file storage for driver packages."""
+import hashlib
+from pathlib import Path
+
+
+class DriverStore:
+    """SHA256 content-addressed file storage for printer driver packages.
+
+    Files are stored as DRIVERS_DIR/{sha256} so identical uploads are
+    deduplicated automatically.
+    """
+
+    def __init__(self, base_dir: str) -> None:
+        self._base = Path(base_dir)
+        self._base.mkdir(parents=True, exist_ok=True)
+
+    def save(self, data: bytes) -> str:
+        """Persist *data* and return its SHA256 hex digest.
+
+        If the file already exists the write is skipped (deduplication).
+        """
+        digest = hashlib.sha256(data).hexdigest()
+        dest = self._base / digest
+        if not dest.exists():
+            dest.write_bytes(data)
+        return digest
+
+    def get_path(self, sha256: str) -> Path:
+        """Return the filesystem path for a given SHA256 digest."""
+        return self._base / sha256
+
+    def exists(self, sha256: str) -> bool:
+        """Return True if the file for *sha256* exists on disk."""
+        return (self._base / sha256).exists()