[Feature]: instant sign in UX

[SHAcollision]

Problem Statement

After scanning the QR code the app:

1. Proceeds to get a successful session
2. Fetches the bootstrap
3. Fetches notifications
4. Fetches profile.json and last_read
5. ... a few other things
   This can take easily over 10 seconds while the user is still looking at the signin QR wondering whether the Pubky Auth was successful.

Proposed Solution

There should be an instantaneous response to a successful PubkyAuth (a simple ✔️ ? confetti? 😄 just something), then a progress bar while all other requests take place.

Feature Area

Authentication / Login

Feature Type

New Feature (doesn't exist yet)

Acceptance Criteria

No response

Design / Mockups

No response

Alternatives Considered

No response

Suggested Priority

None

Additional Context

No response