Improve session title generation

[travisennis]

Summary\nCurrently the title is generated from the user's first message. If the user's first message is to read a file (like prompt.md), the title becomes generic. Instead, use both the user's first prompt and the assistant's first response to generate a better title. Set the title after the first response instead of immediately upon user submission.\n\n## Details\n- Type: feature\n- Priority: 3\n\n## Notes\nCreated: 2026-01-22T00:54:01Z