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>

models.py

@@ -33,8 +33,12 @@ class Nostrable:
 
 class MerchantProfile(BaseModel):
     name: str | None = None
+    display_name: str | None = None
     about: str | None = None
     picture: str | None = None
+    banner: str | None = None
+    nip05: str | None = None
+    lud16: str | None = None
 
 
 class MerchantConfig(MerchantProfile):