Add option to hide sidebar by default (#8515) (#8528)

* Add option to hide sidebar by default (#8515)

Closes https://github.com/FreshRSS/FreshRSS/issues/8515

Changes proposed in this pull request:

- Add `sidebar_hidden_by_default` user preference (default: `false`)
- Add a checkbox in the Display settings page to toggle this preference
- Hide the sidebar on page load in `normal` and `reader` views when the preference is enabled and no session state exists
- Add English translation key; mark all other languages as `TODO` for translators

How to test the feature manually:

1. Go to Settings → Display, tick "Hide sidebar by default", save
2. Go back to the main view (normal or reader): the sidebar should be hidden on load
3. Toggle the sidebar manually — it should open/stay open for the rest of the session
4. Open a new tab: the sidebar should be hidden again
5. Go to Settings → Display, untick the option, save: the sidebar should now be visible on load as usual
6. Check that the sidebar is always visible on Settings pages regardless of the preference

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: PR comment

* Update app/i18n/pl/conf.php

* i18n: fr

* make fix-all

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Inverle <inverle@proton.me>
Co-authored-by: Alexandre Alapetite <alexandre@alapetite.fr>

app/Models/UserConfiguration.php

@@ -54,6 +54,7 @@ declare(strict_types=1);
  * @property bool $icons_as_emojis
  * @property int $simplify_over_n_feeds
  * @property bool $show_nav_buttons
+ * @property bool $sidebar_hidden_by_default
  * @property 'big'|'small'|'none' $mark_read_button
  * @property 'ASC'|'DESC' $sort_order
  * @property 'id'|'c.name'|'date'|'f.name'|'length'|'link'|'rand'|'title' $sort