feat(ops): add database readiness probe

JobTrackerApi/Program.cs

@@ -645,6 +645,23 @@ app.MapGet("/health", (IConfiguration cfg) => Results.Ok(new
     version = BuildMetadata.ResolveVersion(cfg),
 })).AllowAnonymous();
 
+// Readiness is separate from liveness: dependency outages must block a release without causing
+// Docker to restart an otherwise healthy API process. Keep the public response deliberately terse;
+// authorised administrators get detailed database diagnostics from /api/admin/system.
+app.MapGet("/ready", async (JobTrackerContext db, CancellationToken cancellationToken) =>
+{
+    try
+    {
+        return await db.Database.CanConnectAsync(cancellationToken)
+            ? Results.Ok(new { status = "ready" })
+            : Results.Json(new { status = "unavailable" }, statusCode: StatusCodes.Status503ServiceUnavailable);
+    }
+    catch
+    {
+        return Results.Json(new { status = "unavailable" }, statusCode: StatusCodes.Status503ServiceUnavailable);
+    }
+}).AllowAnonymous();
+
 // API schema for tooling/docs. Dev-only: not exposed in production deployments.
 if (app.Environment.IsDevelopment())
 {