Improve model support, selection, streaming, and thinking events.

[Matoo125]

Currently the application uses Claude Agent SDK, there is also a branch with OpenCode. Reason for using these tools, rather than standard provider SDK, is that these tools can review local files. For optimal performance we want to implement and benchmark multiple providers.

• user can select between open-code and claude-agent. Assumptions are that open-code has better DX 90%, and gives us access to more models 100%. Claude Agent SDK cannot stream structured output. Structured output: the JSON result appears only in the final ResultMessage.structured_output, not as streaming deltas. See [structured outputs](https://platform.claude.com/docs/en/agent-sdk/structured-outputs) for details. OpenCode SDK and server docs.
• system can use direct query to provider to increase speed, when no local folder exploration is needed Assumption: we are not able to get the same level of performance with open-code (30%)
• improve Claude Agent SDK implementation by streaming all partial events
• look at skills/tools. agent can have a skill to add rows to database (requirements, assumptions) istead of streaming structured output.