feat(client): add nine interface languages and a searchable language picker

Traditional Chinese cannot reuse the `%two_letters_code%` filename because it would collide with
Simplified under `zh.json`, so `crowdin.yml` maps `zh-TW` to a `zh-Hant` catalog and locale
matching resolves by script subtag before falling back to the base language. Every other new
locale keeps its bare two-letter ID.

Twenty-five entries outgrew the old menus. The mobile submenu inherited `overflow-hidden` with no
max-height, so the last nine languages were unreachable on a phone, and the list was ordered by
ISO code while displaying endonyms, which reads as unsorted. Both header menus now render one
LanguagePicker that searches the native name, the English name and the locale code, groups the
browser's own languages as suggestions, and orders the rest with a collator on the string it
actually shows. Mobile opens a sheet instead of a nested flyout, since a flyout is the wrong
shape for touch regardless of height. Settings gains the Appearance language section its copy
has anticipated since the keys were added.

Tighten the Crowdin progress chart, which the longer language list had stretched to 810px tall.

crowdin.yml

@@ -4,18 +4,27 @@ export_languages:
   - cs
   - da
   - de
+  - el
   - es-ES
   - fi
   - fr
+  - hu
+  - id
   - it
+  - ja
+  - ko
   - nl
   - pl
   - pt-BR
+  - ro
   - ru
+  - sk
   - sl
   - sv-SE
+  - tr
   - uk
   - zh-CN
+  - zh-TW
 
 pull_request_title: "i18n(client): sync translations from Crowdin"
 commit_message: |-
@@ -27,4 +36,7 @@ append_commit_message: false
 files:
   - source: /client/src/locales/en.json
     translation: /client/src/locales/%two_letters_code%.json
+    languages_mapping:
+      two_letters_code:
+        zh-TW: zh-Hant
     update_option: update_as_unapproved