Adds balance payment feature

Implements a feature that allows users to pay their outstanding balance via Lightning.

The changes include:
- Adds the UI elements for invoice generation and display, including QR code.
- Integrates backend endpoints to generate and record payments.
- Adds polling mechanism to track payments and update balance.
- Creates new database models to support manual payment requests.

static/js/index.js

@@ -32,6 +32,8 @@ window.app = Vue.createApp({
       payDialog: {
         show: false,
         amount: null,
+        paymentRequest: null,
+        paymentHash: null,
         loading: false
       },
       settingsDialog: {
@@ -311,39 +313,108 @@ window.app = Vue.createApp({
     async submitPayment() {
       this.payDialog.loading = true
       try {
-        // First, generate an invoice for the payment
-        const invoiceResponse = await LNbits.api.request(
+        // Generate an invoice on the Castle wallet
+        const response = await LNbits.api.request(
           'POST',
-          '/api/v1/payments',
+          '/castle/api/v1/generate-payment-invoice',
           this.g.user.wallets[0].inkey,
           {
-            out: false,
-            amount: this.payDialog.amount,
-            memo: `Payment to Castle - ${this.payDialog.amount} sats`,
-            unit: 'sat'
+            amount: this.payDialog.amount
           }
         )
 
-        // Show the invoice to the user
+        // Show the payment request in the dialog
+        this.payDialog.paymentRequest = response.data.payment_request
+        this.payDialog.paymentHash = response.data.payment_hash
+
         this.$q.notify({
           type: 'positive',
-          message: 'Invoice generated! Pay it to settle your balance.',
-          timeout: 5000
+          message: 'Invoice generated! Scan QR code or copy to pay.',
+          timeout: 3000
         })
 
-        // TODO: After payment, call /castle/api/v1/pay-balance to record it
-        // This would typically be done via a webhook or payment verification
-
-        this.payDialog.show = false
-        this.payDialog.amount = null
+        // Poll for payment completion
+        this.pollForPayment(response.data.payment_hash)
       } catch (error) {
         LNbits.utils.notifyApiError(error)
       } finally {
         this.payDialog.loading = false
       }
     },
+    async pollForPayment(paymentHash) {
+      // Poll every 2 seconds for payment status
+      const checkPayment = async () => {
+        try {
+          const response = await LNbits.api.request(
+            'GET',
+            `/api/v1/payments/${paymentHash}`,
+            this.g.user.wallets[0].inkey
+          )
+
+          if (response.data && response.data.paid) {
+            // Record payment in accounting
+            try {
+              await LNbits.api.request(
+                'POST',
+                '/castle/api/v1/record-payment',
+                this.g.user.wallets[0].inkey,
+                {
+                  payment_hash: paymentHash
+                }
+              )
+            } catch (error) {
+              console.error('Error recording payment:', error)
+            }
+
+            this.$q.notify({
+              type: 'positive',
+              message: 'Payment received! Your balance has been updated.',
+              timeout: 3000
+            })
+            this.payDialog.show = false
+            this.payDialog.paymentRequest = null
+            this.payDialog.amount = null
+            await this.loadBalance()
+            await this.loadTransactions()
+            return true
+          }
+          return false
+        } catch (error) {
+          return false
+        }
+      }
+
+      // Check every 2 seconds for up to 5 minutes
+      let attempts = 0
+      const maxAttempts = 150 // 5 minutes
+      const intervalId = setInterval(async () => {
+        attempts++
+        const paid = await checkPayment()
+        if (paid || attempts >= maxAttempts) {
+          clearInterval(intervalId)
+        }
+      }, 2000)
+    },
+    showManualPaymentOption() {
+      // TODO: Show manual payment request dialog
+      this.$q.notify({
+        type: 'info',
+        message: 'Manual payment feature coming soon!',
+        timeout: 3000
+      })
+    },
+    copyToClipboard(text) {
+      navigator.clipboard.writeText(text)
+      this.$q.notify({
+        type: 'positive',
+        message: 'Copied to clipboard!',
+        timeout: 1000
+      })
+    },
     showPayBalanceDialog() {
       this.payDialog.amount = Math.abs(this.balance.balance)
+      this.payDialog.paymentRequest = null
+      this.payDialog.paymentHash = null
       this.payDialog.show = true
     },
     async showReceivableDialog() {