Language and theme follow the account: PATCH /me for the theme, /me's language by default

The server's /api/v2 now has PATCH /me {language, theme} and /me lists its languages and
themes. The theme is the account's and choosing one saves it there (a refusal is said);
a server whose /me lists no themes keeps the earlier choice in the app. The language is the
account's unless Settings chose this computer's or another (kept in the app, as the phone
does); a change of the account's opens the window again in it, once.

Fixtures re-pinned to the server's dev (f7f2ff2), with the new /api/v2 parity ones.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/ui/fixtures/schedule_run.json

@@ -0,0 +1,52 @@
+{
+  "run": {
+    "id": "run1",
+    "schedule_id": "sched1",
+    "status": "ok",
+    "timing": "late",
+    "missed": 0,
+    "due_at": "2026-01-02T03:04:05+00:00",
+    "started_at": "2026-01-02T03:04:05+00:00",
+    "finished_at": "2026-01-02T03:04:05+00:00",
+    "waiting_for": null,
+    "retry_at": null,
+    "progress": null,
+    "attempts": 1,
+    "model": {
+      "id": "gpt-oss",
+      "name": "GPT-OSS",
+      "reason": "switched",
+      "switched_from": "Qwen"
+    },
+    "tokens": {
+      "prompt": 1200,
+      "completion": 340
+    },
+    "cost": null,
+    "chat_id": "chat1",
+    "message_id": "msg2",
+    "report_path": null,
+    "preview": "All the waybread is wrapped.",
+    "error": null,
+    "notified": true,
+    "notification": {
+      "title": "Waybread check",
+      "body": "All the waybread is wrapped.",
+      "public": {
+        "title": "Waybread check",
+        "body": "Finished"
+      },
+      "actions": [
+        "open",
+        "run_again"
+      ],
+      "labels": {
+        "open": "Open",
+        "run_again": "Run again"
+      },
+      "ask": ""
+    },
+    "watch": null
+  },
+  "text": "All the waybread is *wrapped*."
+}