fix: Persist loaded model and mode on ACP session load

[noamzbr]

Fixes #9828

Fixes my pervious #7809 by also using set model and set mode to change the actual model and mode of the loaded session (verified working this time)

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found the following related PRs that might address similar functionality:

Related PRs:

1. PR fix(acp): persist session state to disk and add isReplay metadata #6563 - fix(acp): persist session state to disk and add isReplay metadata

   • This PR also deals with ACP session persistence, which is related to the current PR's goal of persisting model and mode on session load.

2. PR feat(acp): add session persistence and history replay #5153 - feat(acp): add session persistence and history replay

   • This PR addresses session persistence and replay functionality for ACP, which overlaps with the current PR's persistence concerns.

These PRs are related to session state persistence in ACP, though the current PR (#9829) appears to be addressing a specific issue (#9828) about persisting the loaded model and mode. The previous attempt in PR #7809 is referenced in the description as being fixed by this PR.