feat: tui: Add /init command

[veracioux]

Testing:

• Run /init in home route (no session active): should create a new session and send the usual init prompt
• Run /init in an existing session: should send the usual init prompt
• Bind a keybind to project_init: should work

Closes #3637.

[rekram1-node]

I think we are gonna go with this approach instead: #3677

I think youd agree it makes more sense, prevents us from reimplementing /init for every client we build. Also introduces the ability of someone to pass instructions to /init

[veracioux]

Absolutely!