fix(l10n): consolidate Czech onto the base values-cs qualifier

Czech has a single Crowdin target (cs), but Crowdin's default android_code
for it is cs-rCZ, so the human/Crowdin translation was written to
values-cs-rCZ. Promote it to base values-cs, delete the regional dir, map
cs -> cs in crowdin.yml so future syncs land at the base (single target =>
no collision), and drop cs-CZ from locales_config so the per-app language
picker shows just "Czech".

Also removes the bulk-filled base values-cs from PR #3371 ("Add and update
translations across 50+ locales"), which had translated 38 strings marked
translatable="false" in the source (the *_search_keywords English index,
github/mastodon proper nouns, notification-channel names). The promoted
cs-rCZ is Crowdin-clean (0 translatable="false" leakage), so this also
fixes that contamination for Czech.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KhEN93aKyQCFVpLUgRNXid

amethyst/src/main/res/xml/locales_config.xml

@@ -4,7 +4,6 @@
     <locale android:name="ar-SA"/>
     <locale android:name="bn-BD"/>
     <locale android:name="cs"/>
-    <locale android:name="cs-CZ"/>
     <locale android:name="cy-GB"/>
     <locale android:name="da-DK"/>
     <locale android:name="de"/>

crowdin.yml

@@ -21,4 +21,8 @@ files:
     #     values-sw-rTZ.
     languages_mapping:
       android_code:
+        # Czech: single target, but Crowdin's default android_code is cs-rCZ, so
+        # without this it writes values-cs-rCZ instead of base values-cs. Single
+        # target => no collision; cs-CZ is dropped from locales_config to match.
+        cs: cs
         sw-KE: sw