fix: make transcode leases ownership-checked and cleanup-aware

Cleanup never matched a live session because the controller registered empty
manifest and segment paths, renewal was a read-modify-write that could revert a
takeover, and the takeover script compared an ISO date to a number, so it errored.

- populate the session record's manifest and segment paths from the playlist path
- renew the lease via a Lua compare-and-set on the owning pod
- store the lease expiry as unix milliseconds so the scripts can compare it
- retain the session record past its lease so an orphan can still be taken over
- test the Redis store against a real Redis, including the renew-vs-takeover race
- drop the live stream record nothing ever read back

MediaBrowser.Controller/MediaEncoding/TranscodeStoreOptions.cs

@@ -16,4 +16,11 @@ public sealed class TranscodeStoreOptions
     /// Gets or sets the duration in seconds for which a transcoding session lease is valid.
     /// </summary>
     public int LeaseDurationSeconds { get; set; } = 30;
+
+    /// <summary>
+    /// Gets or sets how long in seconds a session record is retained after its lease was last renewed.
+    /// The record must outlive the lease, otherwise an orphaned session is gone before another pod
+    /// can take it over.
+    /// </summary>
+    public int SessionRetentionSeconds { get; set; } = 300;
 }