fix(api): newest-first season and episode order

DESIGN.md §9.6 now puts the current season at the top: seasons
descend by number within a series (season 0 lands last under plain
numeric descending) and episodes descend within each season. Changed
the two queries in load_seasons; the SPA renders this order as given.

arr-compat checked and untouched: it reads seasons with its own
ORDER BY number query straight from the database, never through
arr-api, and SeasonResource carries season_number, which Jellyseerr
matches on rather than position. Sonarr's real API also returns
seasons ascending, so the shim keeps the contract it emulates.

The existing vanished-flag test indexed seasons positionally; it now
looks them up by number so it tests the flag, not the order. New test
asserts [2, 1, 0] for seasons and descending episodes within each.
.sqlx regenerated via just db-prepare. just ci green locally.

.sqlx/query-f52980596624a03ae4c704926a443c5665c865f9d3d3699105790fe09d8b3fc9.json

@@ -0,0 +1,44 @@
+{
+  "db_name": "SQLite",
+  "query": "SELECT id AS \"id!: i64\", series_id AS \"series_id!: i64\", number AS \"number!: i64\", tracked AS \"tracked!: bool\", vanished AS \"vanished!: bool\" FROM seasons WHERE series_id = ? ORDER BY number DESC",
+  "describe": {
+    "columns": [
+      {
+        "name": "id!: i64",
+        "ordinal": 0,
+        "type_info": "Integer"
+      },
+      {
+        "name": "series_id!: i64",
+        "ordinal": 1,
+        "type_info": "Integer"
+      },
+      {
+        "name": "number!: i64",
+        "ordinal": 2,
+        "type_info": "Integer"
+      },
+      {
+        "name": "tracked!: bool",
+        "ordinal": 3,
+        "type_info": "Integer"
+      },
+      {
+        "name": "vanished!: bool",
+        "ordinal": 4,
+        "type_info": "Integer"
+      }
+    ],
+    "parameters": {
+      "Right": 1
+    },
+    "nullable": [
+      true,
+      false,
+      false,
+      false,
+      false
+    ]
+  },
+  "hash": "f52980596624a03ae4c704926a443c5665c865f9d3d3699105790fe09d8b3fc9"
+}