[FEAT] Support NIP-07 browser extension login instead of pasting nsec

[BenGWeeks]

Problem

Currently, when a user wants to log in to place orders, the marketplace prompts them to paste their Nostr private key (nsec) directly into a text field.

This is a security concern because:

• The private key is exposed to the website and could be logged, stolen, or leaked
• Users must fully trust the LNbits operator with their Nostr identity
• There's no isolation between the key and the web application
• Keys stored in localStorage are accessible to browser extensions and vulnerable to XSS attacks

Proposed Solution

Implement NIP-07 support to allow users to sign in using browser extensions like:

• Alby
• nos2x
• Flamingo

With NIP-07, the private key never leaves the secure extension. The website only requests signatures when needed, and the user approves each request.

Implementation Notes

The standard approach is to check for window.nostr and use:

// Check if extension is available
if (window.nostr) {
  // Get public key
  const pubkey = await window.nostr.getPublicKey();
  
  // Sign events when needed
  const signedEvent = await window.nostr.signEvent(event);
}

Similar functionality should be added to https://github.com/EdenWeeks/eden-weeks-art as well.

Additional Context

• The "Generate" button for creating ephemeral keys is fine for testing/browsing
• For users who want to use their real Nostr identity, NIP-07 is the secure standard
• Consider also supporting NIP-46 (Nostr Connect) for remote signing