fix: network-share readers, model unload off the loop, bad save requests (#620)

Every read-only SQLite open now uses one URI helper, so a library on a Windows
network share works in backups, restores, moves and history reads. Unloading a
model no longer blocks the server. A malformed /save body gets a 400, not a 500.

tests/test_sqlite_uri.py

@@ -0,0 +1,39 @@
+"""Every read-only SQLite open uses one URI helper (#620).
+
+pathlib writes a Windows network path as ``file://server/share/x.db``, which
+SQLite refuses. A reader that builds its own URI breaks backups, restores,
+library moves or history reads for a library on a network share.
+"""
+
+import re
+import sys
+import unittest
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(ROOT))
+
+from database.sqlite_uri import readonly_uri  # noqa: E402
+
+
+class TestReadonlyUri(unittest.TestCase):
+    def test_a_network_path_has_an_empty_authority(self):
+        self.assertEqual(
+            readonly_uri(r"\\server\share\Comfy UI\prompts.db", windows=True),
+            "file:////server/share/Comfy%20UI/prompts.db?mode=ro",
+        )
+
+    def test_no_reader_builds_its_own_uri(self):
+        offenders = []
+        for folder in ("database", "py", "utils"):
+            for path in (ROOT / folder).rglob("*.py"):
+                if path.name == "sqlite_uri.py":
+                    continue
+                text = path.read_text(encoding="utf-8")
+                if re.search(r"as_uri\(\)\s*\+\s*[\"']\?mode=ro", text):
+                    offenders.append(path.relative_to(ROOT).as_posix())
+        self.assertEqual(offenders, [])
+
+
+if __name__ == "__main__":
+    unittest.main()