[codex] Fix chat bubble width and realtime transcript duplicates

[oscharko]

Summary

• Fix right-aligned user chat bubbles so short sentences do not wrap into artificially narrow columns.
• Deduplicate realtime assistant transcripts when the provider mirrors the same text through multiple event shapes.
• Add regression coverage for mirrored realtime transcript events and repeated text across separate user turns.

Validation

• npm --workspace @oscharko-dev/keiko-ui test -- src/app/components/desktop/hooks/useRealtimeVoice.test.ts src/app/components/desktop/ChatWindow.test.tsx
• npm --workspace @oscharko-dev/keiko-ui run typecheck
• git diff --check