feat: add merchant profile panel to Merchant tab

Display merchant profile information with:
- Banner image or grey placeholder
- Profile avatar with shadow
- Display name (or name fallback)
- About description
- NIP-05 verified identity indicator
- Lightning address (LUD16)

Extends MerchantProfile model with new fields:
display_name, banner, nip05, lud16

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

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

static/components/merchant-tab.js

@@ -10,7 +10,8 @@ window.app.component('merchant-tab', {
     'merchant-active',
     'public-key',
     'private-key',
-    'is-admin'
+    'is-admin',
+    'merchant-config'
   ],
   computed: {
     marketClientUrl: function () {