[Nostr] Add profile management and identity switching

[shadowbipnode]

[Nostr] Add profile management and identity switching

Goal

Replace the current single-profile Nostr architecture with a proper identity management system.

Current situation

Zap Browser currently supports only one hardcoded Nostr identity:

• nostr_profile WHERE id=1
• no logout
• no profile removal
• no profile switching
• no identity isolation

This creates UX and security limitations for a browser intended to be Nostr-native.

Why this matters

Real users often operate multiple Nostr identities:

• personal profile
• anonymous profile
• work/dev profile
• Bitcoin-only profile

Without profile management:

• users cannot rotate identities safely
• corrupted profiles are difficult to recover
• onboarding becomes fragile
• testing different identities is cumbersome
• future permission systems become harder to implement cleanly

Tasks

Database layer

• Replace nostr_profile single-entry assumptions.
• Support multiple stored profiles.
• Add active profile state.
• Add migration path from legacy id=1 schema.

Identity management

• Add profile import/remove/logout.
• Add profile switching.
• Add active profile persistence across restarts.
• Ensure NIP-07 uses the currently active identity.

UI/UX

• Add profile management screen.
• Add “Disconnect profile” button.
• Add “Switch identity” flow.
• Show active identity in browser UI.

Security

• Ensure encrypted private keys remain isolated per profile.
• Prevent accidental cross-profile signing.
• Clear cached permissions on profile switch.

Acceptance criteria

• Users can manage multiple Nostr identities.
• Active identity can be switched without restart.
• NIP-07 correctly reflects the selected profile.
• Profiles can be safely removed.
• Existing users are migrated automatically.

Priority

High.

This is a foundational feature for a sovereign/Nostr-native browser.