Auto-provision merchant from account keypair on first access

The LNbits user account IS the merchant identity. GET /api/v1/merchant
now auto-creates the merchant record using the account's existing Nostr
keypair if one doesn't exist yet, so the extension is immediately
usable without any setup screen.

- Extract _auto_create_merchant() helper used by both GET and POST
- Remove welcome/key-generation screen (replaced with loading spinner)
- Remove dead frontend code (generateKeys, importKeys dialogs)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

static/js/index.js

@@ -13,19 +13,6 @@ window.app = Vue.createApp({
       orderPubkey: null,
       showKeys: false,
       stallCount: 0,
-      importKeyDialog: {
-        show: false,
-        data: {
-          privateKey: null
-        }
-      },
-      generateKeyDialog: {
-        show: false,
-        privateKey: null,
-        nsec: null,
-        npub: null,
-        showNsec: false
-      },
       wsConnection: null,
       nostrStatus: {
         connected: false,
@@ -49,23 +36,6 @@ window.app = Vue.createApp({
     }
   },
   methods: {
-    generateKeys: async function () {
-      // No longer need to generate keys here - the backend will use user's existing keypairs
-      await this.createMerchant()
-    },
-    importKeys: async function () {
-      this.importKeyDialog.show = false
-      // Import keys functionality removed since we use user's native keypairs
-      // Show a message that this is no longer needed
-      this.$q.notify({
-        type: 'info',
-        message: 'Merchants now use your account Nostr keys automatically. Key import is no longer needed.',
-        timeout: 3000
-      })
-    },
-    showImportKeysDialog: async function () {
-      this.importKeyDialog.show = true
-    },
     toggleShowKeys: function () {
       this.showKeys = !this.showKeys
     },
@@ -379,7 +349,11 @@ window.app = Vue.createApp({
     }
   },
   created: async function () {
-    await this.getMerchant()
+    const merchant = await this.getMerchant()
+    if (!merchant) {
+      // Auto-create merchant using the account's existing Nostr keypair
+      await this.createMerchant()
+    }
     await this.checkNostrStatus()
     setInterval(async () => {
       if (