feat(feedback): snapshot the sender's language and connector bot at submit

Store the sender's interface language (lang) and, for a message that arrived
through an external connector (Telegram), the bot language (channel_lang) on the
feedback row at submit time, so the operator console shows the state as it was
rather than the account's current settings (same snapshot discipline as a
suspension reason). Added additively in migration 00005. The console detail reads
these columns instead of loading the account live.

backend/internal/postgres/migrations/00004_feedback.sql

@@ -15,7 +15,8 @@ SET search_path = backend, pg_catalog;
 -- attachment is the raw bytes (capped at 1,000,000 in Go); attachment_name carries the original
 -- file name (its extension drives the safe content-type at serve time). sender_ip is the
 -- gateway-forwarded client IP (validated, like chat); channel is the submitting platform
--- (telegram/ios/android/web, validated in Go).
+-- (telegram/ios/android/web, validated in Go). The sender's interface/bot language snapshots
+-- (lang, channel_lang) are added additively in 00005.
 CREATE TABLE feedback_messages (
     message_id      uuid        PRIMARY KEY,
     account_id      uuid        NOT NULL REFERENCES accounts (account_id) ON DELETE CASCADE,