feat(ui): implement suggested UI improvements

chore(ui): modefied theme, error message and placeholder

feat(ui): opening message in chat

feat(ui): clear input textbox before chat output

for load test

fix: modify log

fix: modify log

feat: modify Global TPM calculation

feat: add token usage record list

feat: add global tpm tracker

fix: modify for error handling

modify: change default_concurrency_limit

fix: add token calculate log

fix: remove current_chat_id and migrate to use session_state to prevent var missuse across sessions

improve-readaility (#7)