Implement isolated multi-profile browser architecture

[shadowbipnode]

Goal
Allow users to create multiple isolated browser identities.

Profiles may include:

• separate Nostr identities
• separate NWC wallets
• separate cookies/storage
• separate privacy settings
• separate user-agents

Example profiles:

• Sovereign
• Anonymous
• Work
• Burner
• Lightning

Tasks

• Design profile storage architecture
• Create profile switcher
• Separate session persistence
• Isolate BrowserView/session data
• Persist per-profile settings
• Add profile creation UI

Acceptance criteria

• Profiles are isolated
• Switching is fast
• Permissions are profile-specific
• Browser remains stable with multiple profiles