apply: define LANGUAGE setting (fixes 500 on first handled ApplicationResult)

apply/language.py references LANGUAGE via \`from settings import *\`, but
the constant was never added to apply/settings.py. Python only errored at
the first runtime use — which is \`str(ApplicationResult)\` in the /apply
handler. Any outcome that didn't short-circuit before the final \`return
ApplyResponse(message=str(result), …)\` blew up with NameError → 500.

Add LANGUAGE = getenv("LANGUAGE", "de") so existing translations.toml
keys resolve. Reproduced live inside the apply container: NameError:
name 'LANGUAGE' is not defined at language.py:15.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apply/settings.py

@@ -46,6 +46,10 @@ POST_SUBMISSION_SLEEP_MS: int = get_int_env("POST_SUBMISSION_SLEEP_MS", "0")
 # --- Service -----------------------------------------------------------------
 INTERNAL_API_KEY: str = get_env_or_fail("INTERNAL_API_KEY")
 
+# --- Translations ------------------------------------------------------------
+# Key into translations.toml (e.g. "de", "en"). Used by language.get_text.
+LANGUAGE: str = getenv("LANGUAGE", "de")
+
 
 def log_settings() -> None:
     logger.debug("--- Settings ---")