feat: add zap button with lightning invoice modal and fix keys detection

- Add Zap button to film detail modal with LNURL-pay invoice generation
- Create ZapModal with 4 preset amounts, custom input, and QR code display
- Fix hasPrivateKey detection for production builds (use instanceof)
- Fix KeysModal header centering (pr-8 → px-8)
- Update most-zapped algorithm to track real Nostr zap receipts (kind 9735)
- Add BOLT11 amount decoder and zap receipt relay subscription

Co-authored-by: Cursor <cursoragent@cursor.com>

src/composables/useContentDiscovery.ts

@@ -26,11 +26,44 @@ export interface ContentStats {
   minusCount: number
   commentCount: number
   reviewCount: number
+  zapCount: number
+  zapAmountSats: number
   recentEvents: NostrEvent[]
 }
 
 const SEVEN_DAYS = 7 * 24 * 60 * 60
 
+/**
+ * Decode the amount in satoshis from a BOLT11 invoice string.
+ * BOLT11 encodes the amount after 'lnbc' with a multiplier suffix:
+ *   m = milli (0.001), u = micro (0.000001), n = nano, p = pico
+ * Returns 0 if the amount cannot be parsed.
+ */
+function decodeBolt11Amount(bolt11: string): number {
+  try {
+    const lower = bolt11.toLowerCase()
+    // Match: lnbc<amount><multiplier>1...
+    const match = lower.match(/^lnbc(\d+)([munp]?)1/)
+    if (!match) return 0
+
+    const value = parseInt(match[1], 10)
+    if (isNaN(value)) return 0
+
+    const multiplier = match[2]
+    // Convert BTC amount to sats (1 BTC = 100,000,000 sats)
+    switch (multiplier) {
+      case 'm': return value * 100_000     // milli-BTC
+      case 'u': return value * 100         // micro-BTC
+      case 'n': return Math.round(value * 0.1) // nano-BTC
+      case 'p': return Math.round(value * 0.0001) // pico-BTC
+      case '':  return value * 100_000_000 // whole BTC
+      default:  return 0
+    }
+  } catch {
+    return 0
+  }
+}
+
 // --- Shared Module State (singleton) ---
 
 const activeAlgorithm = ref<AlgorithmId>(null)
@@ -57,6 +90,8 @@ function rebuildStats() {
         minusCount: 0,
         commentCount: 0,
         reviewCount: 0,
+        zapCount: 0,
+        zapAmountSats: 0,
         recentEvents: [],
       }
       map.set(id, stats)
@@ -93,6 +128,30 @@ function rebuildStats() {
     }
   }
 
+  // Process zap receipts (kind 9735) from the EventStore.
+  // Zap receipts reference content via the 'i' tag (external identifiers)
+  // or via embedded zap request description.
+  const zapReceipts = eventStore.getByFilters([{ kinds: [9735] }])
+  if (zapReceipts) {
+    for (const event of zapReceipts) {
+      // Try to find the external content ID from the zap receipt tags
+      const externalId = getTagValue(event, 'i')
+      if (!externalId) continue
+
+      const stats = getOrCreate(externalId)
+      stats.zapCount++
+
+      // Extract amount from the bolt11 tag if present
+      const bolt11 = getTagValue(event, 'bolt11')
+      if (bolt11) {
+        const sats = decodeBolt11Amount(bolt11)
+        if (sats > 0) stats.zapAmountSats += sats
+      }
+
+      stats.recentEvents.push(event)
+    }
+  }
+
   contentStatsMap.value = map
 }
 
@@ -129,6 +188,17 @@ function initSubscriptions() {
     })
   subscriptionRefs.push(commentSub)
 
+  // Subscribe to zap receipts (kind 9735) that reference external web content.
+  // These are published by LNURL providers when a zap is paid.
+  const zapSub = pool
+    .subscription(currentRelays, [{ kinds: [9735] }])
+    .pipe(onlyEvents(), mapEventsToStore(eventStore))
+    .subscribe({
+      next: () => rebuildStats(),
+      error: (err) => console.error('Discovery zap subscription error:', err),
+    })
+  subscriptionRefs.push(zapSub)
+
   // Initial build from any already-cached events
   rebuildStats()
 
@@ -145,6 +215,8 @@ const EMPTY_STATS: ContentStats = {
   minusCount: 0,
   commentCount: 0,
   reviewCount: 0,
+  zapCount: 0,
+  zapAmountSats: 0,
   recentEvents: [],
 }
 
@@ -263,11 +335,20 @@ function sortContentEntries(
       )
     }
 
-    case 'most-zapped':
+    case 'most-zapped': {
+      // Sort by total sats zapped first, then by zap count,
+      // falling back to positive reactions if no zap data exists.
+      const zapScore = (stats: ContentStats) =>
+        stats.zapAmountSats > 0
+          ? stats.zapAmountSats
+          : stats.zapCount > 0
+            ? stats.zapCount * 100 // Weight each zap receipt as 100 sats
+            : stats.plusCount       // Fallback to likes if no zaps yet
       return [...entries].sort(
         (a: [Content, ContentStats], b: [Content, ContentStats]) =>
-          b[1].plusCount - a[1].plusCount,
+          zapScore(b[1]) - zapScore(a[1]),
       )
+    }
 
     case 'most-reviews':
       return [...entries].sort(