feat(api): move title files on root change

Changing a movie's or series' root previously rewrote root_id and left
the files behind, so the §7.4 layout stopped describing the disk and
the root's policy applied to a library the files were not in. Series
had no root control at all.

All roots share one ZFS dataset, so the move is a rename of the title
folder into the new root, never a copy — hardlinks and the seeding
torrent survive it (§7.3). Disk first, row second: a destination that
already holds the folder is a 409, a failed rename leaves the row
unchanged, and a title with nothing on disk moves with no filesystem
work. media_files rows are rewritten in the same transaction as the
root_id, and a successful move triggers the §7.5 Jellyfin refresh.

Issue #228

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.sqlx/query-6ef45d7e6fc113b578fab91148f9ab5455e7a2d06fc86291e2c6c9696fd08953.json

@@ -0,0 +1,26 @@
+{
+  "db_name": "SQLite",
+  "query": "SELECT path AS \"path!: String\" FROM roots WHERE id = ?",
+  "describe": {
+    "columns": [
+      {
+        "name": "path!: String",
+        "ordinal": 0,
+        "type_info": "Text",
+        "origin": {
+          "Table": {
+            "table": "roots",
+            "name": "path"
+          }
+        }
+      }
+    ],
+    "parameters": {
+      "Right": 1
+    },
+    "nullable": [
+      false
+    ]
+  },
+  "hash": "6ef45d7e6fc113b578fab91148f9ab5455e7a2d06fc86291e2c6c9696fd08953"
+}