feat: Onboarding Prototype

[joybytes]

This PR contain commits for implementation of the onboarding prototype

Document of requirements: https://docs.google.com/document/d/1SqJPmZBk94Z9UYAONJaO-YGe495amLoIrSDdNvZkKwk/edit?tab=t.0

Mural flow: https://app.mural.co/t/gaap0347/m/gaap0347/1742822810786/d263343cf1f4e55f080cceb8962ff7436d1f32d0

Backlink expectation for Sender Email Journey:

#	From Name Present	Reply-to Addresses	Action	Forward Navigation	Back Navigation	Status
1	❌ No	❌ None	Do it later	From name → Let recipients → Add recipients	Add recipients → Let recipients → From name → View templates	✅ PASSED
2	❌ No	❌ None	Add + Verify	From name → Let recipients → Add reply → Verify → Add recipients	Add recipients → View templates	✅ PASSED
3	❌ No	✅ Single	–	From name → Add recipients	Add recipients → From name → View templates	✅ PASSED
4	❌ No	✅ Multiple	Choose reply-to	From name → Choose a reply-to → Add recipients	Add recipients → Choose a reply-to → From name → View templates	✅ PASSED
5	✅ Yes	❌ None	Do it later	Let recipients → Add recipients	Add recipients → Let recipients → View templates	✅ PASSED
6	✅ Yes	❌ None	Add + Verify	Let recipients → Add reply → Verify → Add recipients	Add recipients → View templates	✅ PASSED
7	✅ Yes	✅ Single	–	→ Add recipients	Add recipients → View templates	✅ PASSED
8	✅ Yes	✅ Multiple	Choose reply-to	Choose a reply-to → Add recipients	Add recipients → Choose a reply-to → View templates	✅ PASSED