fix(ha): read transcode store config from the variable form deployments set

The startup configuration only reads JELLYFIN_ prefixed environment
variables, so the bare Jellyfin__TranscodeStore__* form used by the chart,
the manifests and the README is dropped and the Redis store is never
registered. Nothing logs the selected store, so the fallback is invisible.

- Read bare Jellyfin__* variables into the Jellyfin:* configuration root
- Keep an explicit JELLYFIN_ variable winning over the bare form
- Log the selected transcode session store at startup
- Ping Redis once at startup and log an unreachable store at Error
- Log endpoints only, never the connection string

Jellyfin.Server/Program.cs

@@ -391,6 +391,8 @@ namespace Jellyfin.Server
                 .AddInMemoryCollection(inMemoryDefaultConfig)
                 .AddJsonFile(LoggingConfigFileDefault, optional: false, reloadOnChange: true)
                 .AddJsonFile(LoggingConfigFileSystem, optional: true, reloadOnChange: true)
+                // Added before the prefixed source so an explicit JELLYFIN_ variable still wins.
+                .AddJellyfinSectionEnvironmentVariables()
                 .AddEnvironmentVariables("JELLYFIN_")
                 .AddInMemoryCollection(commandLineOpts.ConvertToConfig());
         }