feat: multi-profile support and UI improvements

- Remove backend restriction on one merchant per user
- Add "Generate New Key" dialog with npub/nsec display
- Add "Import Existing Key" option with duplicate check
- Change "Save" to "Save & Publish" in edit profile dialog
- Remove standalone Publish button (now part of Save)
- Add trash icon to saved profile for removal
- Show display_name in saved profiles dropdown
- Hide nsec by default with eye toggle in generate dialog

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

views_api.py

@@ -98,9 +98,6 @@ async def api_create_merchant(
         merchant = await get_merchant_by_pubkey(data.public_key)
         assert merchant is None, "A merchant already uses this public key"
 
-        merchant = await get_merchant_for_user(wallet.wallet.user)
-        assert merchant is None, "A merchant already exists for this user"
-
         merchant = await create_merchant(wallet.wallet.user, data)
 
         await create_zone(