fix: model select showed a value that was never saved

Root cause of "設定値が不正です (モデルが設定されていません)" despite the
settings UI showing a selected model:
- fillModels(models, selected="") never set option.selected when no model
  was saved yet. The browser then auto-selects the first option visually,
  so the UI displayed e.g. "glm-5.3:cloud" while storage.model remained
  empty. Translation therefore failed with the no-model error until the
  user pressed Save, which materialized the UI value into storage.

Fixes
- popup.js/options.js fillModels: when no model is saved and the list is
  non-empty, explicitly select the first model so the UI value always
  matches what will be used
- popup.js: after the model list loads, persist the auto-selected model
  if storage still has none
- options.js loadSettings: same sync after loadModels, so opening the
  options page also heals the empty-model state

Results: 73 passed, 0 failed. dist rebuilt.

0 files changed, 0 insertions, 0 deletions