Replace the AI chat typing indicator text "AI is typing…" with
"Thinking…".
- typing-indicator.tsx: use t("Thinking…") instead of t("AI is typing…")
- en-US: drop the now-redundant "AI is typing…" key (the "Thinking…"
key already existed and was unused)
- ru-RU: rename the key to "Thinking…" with value "Думаю…"
- update related comments in message-list.tsx and the test file
ccbd3e1962
