fix: block combo signals during project creation to prevent old project flash

[boscorat]

Summary

When creating a new project, the old project’s info was briefly visible before the new project selection fired and updated the UI. This was caused by model.select() in _finalise_project_add triggering currentIndexChanged with an intermediate index while the combo box re-queried the database.

Changes

• project_presenter.py: Added project_switched signal and wrapped model.select() + setCurrentIndex() in a signal-blocking block to prevent intermediate index emissions. Emits project_switched after unblocking to trigger a single, clean UI update.
• stan_presenter.py: Connected project_switched to update_current_project_info.

This follows the same pattern used in admin_presenter.py:refresh_combos for signal blocking.

Testing

• ruff check — clean
• ruff format --check — clean
• pyrefly check — clean (0 errors)
• pytest — 146/146 passed

Closes #167

[Copilot]

🟡 Changes recommended

The new project_switched wiring bypasses existing project-switch handling and the emitted index should be synchronized with the combo’s actual selected index.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR fixes a brief UI “flash” of the previously selected project during new-project creation by preventing intermediate currentIndexChanged emissions while the project combo box is being refreshed.

Changes:

• Adds a project_switched signal and blocks combo-box signals around model.select() + setCurrentIndex() during project creation.
• Hooks the new signal into StanPresenter to trigger a single UI refresh after the combo update completes.

File summaries

File	Description
src/openstan/presenters/project_presenter.py	Blocks combo signals during _finalise_project_add and emits a dedicated post-switch signal.
src/openstan/presenters/stan_presenter.py	Connects the new post-switch signal into the presenter to refresh current-project UI.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Lite

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