Adds `default_open_behavior` which let's users control which action
should be the default (add to existing window/open a new window)

TODO:
- [x] Use sensible icon (not `IconName::Screen`) when
`default_open_behavior` is set to `new_window`
- [x] Tweak wording for actions in recent projects menu
<img width="420" height="59" alt="image"
src="https://github.com/user-attachments/assets/69ef112e-bf20-4dd1-9994-e4442266ef87"
/>


Release Notes:

- Added `default_open_behavior` which controls which action (add to
sidebar/open in new window) should be the default when selecting a
project from the recent projects menu

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Co-authored-by: Danilo Leal <daniloleal09@gmail.com>