Restyle the startup UI and add a generic startup activity line

Restyle the startup/migration holding page to match the Jellyfin dark theme,
with the inline wordmark logo, a gradient spinner and a recolored startup log
tree, and move the Morestachio template rendering into a reusable
StartupUiRenderer.

Add a curated, non-identifying "current activity" line to the always-visible
header (for example "Initializing server" or "Running migration X of Y"),
reported from the startup flow and the migration service so it never leaks
server details to unauthenticated clients. Move the log download into a
"Download logs" link in the log panel header, and show only the header, with
no log hints, to non-local clients.

1 files changed, 44 insertions, 0 deletions

diff --git a/Jellyfin.Server/ServerSetupApp/StartupActivity.cs b/Jellyfin.Server/ServerSetupApp/StartupActivity.cs
new file mode 100644
index 0000000000..5baaf1d40a
--- /dev/null
+++ b/Jellyfin.Server/ServerSetupApp/StartupActivity.cs
@@ -0,0 +1,44 @@
+using System.Globalization;
+
+namespace Jellyfin.Server.ServerSetupApp;
+
+/// <summary>
+/// A curated vocabulary of generic, non-identifying descriptions of what the server is doing during startup.
+/// These are shown in the always-visible header of the startup UI to <b>unauthenticated</b> clients, so every
+/// value must stay generic and must never contain server specific details (paths, names, plugin or migration ids, counts of items, etc.).
+/// </summary>
+public static class StartupActivity
+{
+    /// <summary>The default state before any work has been reported.</summary>
+    public const string Starting = "Starting up";
+
+    /// <summary>Validating that the configured storage locations are usable.</summary>
+    public const string CheckingStorage = "Checking storage";
+
+    /// <summary>Bringing up the migration subsystem and running early startup checks.</summary>
+    public const string Initializing = "Initializing server";
+
+    /// <summary>Preparing the system for migrations (e.g. taking safety backups).</summary>
+    public const string PreparingMigrations = "Preparing migrations";
+
+    /// <summary>Applying database/system migrations without a known count.</summary>
+    public const string ApplyingMigrations = "Applying migrations";
+
+    /// <summary>Restoring from a backup.</summary>
+    public const string RestoringBackup = "Restoring backup";
+
+    /// <summary>Bringing up core services and plugins.</summary>
+    public const string InitializingServices = "Initializing services";
+
+    /// <summary>Running the final startup tasks.</summary>
+    public const string FinishingStartup = "Finishing startup";
+
+    /// <summary>
+    /// Builds a generic "Running migration X of Y" description. Only the numeric position and total are exposed.
+    /// </summary>
+    /// <param name="current">The 1-based index of the migration currently running.</param>
+    /// <param name="total">The total number of migrations in this batch.</param>
+    /// <returns>A generic progress description.</returns>
+    public static string Migration(int current, int total)
+        => string.Format(CultureInfo.InvariantCulture, "Running migration {0} of {1}", current, total);
+}