fix iOS demo round timing

mobile/ios-app/App/HermesRepository.swift

@@ -1,3 +1,4 @@
+import AVFoundation
 import Combine
 import Foundation
 
@@ -239,9 +240,12 @@ enum MockHermesData {
         winningOutcomeID: String,
         now: Date
     ) -> HermesRound {
-        let lockAt = now.addingTimeInterval(15)
-        let settleAt = lockAt.addingTimeInterval(6)
         let mediaURL = localMediaURL(named: "example-round.mov") ?? fallbackMediaURL
+        let previewDurationMs = assetDurationMs(url: mediaURL) ?? 15_000
+        let revealURL = revealMediaURL()
+        let revealDurationMs = assetDurationMs(url: revealURL) ?? 6_000
+        let lockAt = now.addingTimeInterval(Double(previewDurationMs) / 1_000.0)
+        let settleAt = lockAt.addingTimeInterval(6)
 
         let event = HermesEvent(
             id: UUID(uuidString: eventID) ?? UUID(),
@@ -251,9 +255,9 @@ enum MockHermesData {
             titleSv: promptKey,
             status: "active",
             previewStartMs: 0,
-            previewEndMs: 12_000,
-            revealStartMs: 12_000,
-            revealEndMs: 18_000,
+            previewEndMs: previewDurationMs,
+            revealStartMs: 0,
+            revealEndMs: revealDurationMs,
             lockAt: lockAt,
             settleAt: settleAt
         )
@@ -264,11 +268,11 @@ enum MockHermesData {
             mediaType: "hls_main",
             hlsMasterUrl: mediaURL,
             posterUrl: nil,
-            durationMs: 18_000,
+            durationMs: previewDurationMs,
             previewStartMs: 0,
-            previewEndMs: 12_000,
-            revealStartMs: 12_000,
-            revealEndMs: 18_000
+            previewEndMs: previewDurationMs,
+            revealStartMs: 0,
+            revealEndMs: revealDurationMs
         )
 
         let marketUUID = UUID(uuidString: marketID) ?? UUID()
@@ -336,4 +340,13 @@ enum MockHermesData {
         let candidate = repoRoot.appendingPathComponent(fileName)
         return FileManager.default.fileExists(atPath: candidate.path) ? candidate : nil
     }
+
+    private static func assetDurationMs(url: URL) -> Int? {
+        let duration = AVAsset(url: url).duration.seconds
+        guard duration.isFinite, duration > 0 else {
+            return nil
+        }
+
+        return Int((duration * 1_000.0).rounded())
+    }
 }