feat: add dynamic window titles based on user messages

[aryasaatvik]

Summary

• Adds dynamic window title generation that shows the user's message in the terminal title bar while AI is processing
• Implements AI-powered title generation using fast models (Haiku for Anthropic, GPT-4o-mini for OpenAI)
• Window title reverts to "opencode" when AI finishes processing or when session is interrupted

Implementation Details

• Added /session_generate_title endpoint in TypeScript server
• Created title-window.txt prompt file for concise title generation
• Integrated window title updates in Go TUI client
• Title generation happens asynchronously without blocking message submission
• Handles edge cases like session interruption, session switching, and model selection

Test Plan

• [x] Test window title updates when submitting messages
• [x] Verify title reverts to "opencode" when AI completes
• [x] Test title reset on session interrupt (Ctrl+C)
• [x] Verify title resets when switching sessions
• [x] Test fallback to truncated message if API fails
• [x] Ensure title generation works with different providers (Anthropic, OpenAI)

https://github.com/user-attachments/assets/32d3f521-70db-42f4-b129-71dab67be3fe

[thdxr]

this is very cool

i want to clean up our system for doing conditional stuff per provider so let me play with that first before i merge this

[aryasaatvik]

this is very cool

i want to clean up our system for doing conditional stuff per provider so let me play with that first before i merge this

thank you! for smaller tasks like generating verbs and window title i think it would be better to store 2 models (lightweight and main) in the config. i will finish https://github.com/sst/opencode/pull/279 tomorrow