ci(i18n): translation parity guard + allow partial translations

Add scripts/check_translations.py and a lightweight Translations workflow
that runs it (no Android SDK needed) so Weblate PRs get fast feedback. The
script fails on stale keys (present in a translation but not the base) and on
translating translatable="false" entries; missing keys are reported as
coverage only.

Downgrade lint's MissingTranslation to informational: partial community
translations are expected and fall back to the English base at runtime.
Stale/extra keys (ExtraTranslation) remain fatal in lintDebug.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/build.gradle.kts

@@ -78,6 +78,15 @@ android {
         }
     }
 
+    lint {
+        // Community translations are expected to be partial — a missing string
+        // falls back to the English base at runtime — so don't fail the build on
+        // it. Stale/extra keys (ExtraTranslation) stay fatal; scripts/
+        // check_translations.py guards the same invariants with clearer,
+        // translator-facing messages.
+        informational += "MissingTranslation"
+    }
+
     testOptions {
         unitTests {
             all { it.useJUnitPlatform() }