Add zip upload and mapped-path picker for outline import

Sandbox source paths under a configured Imports:RootPath, browse it
from the web dialog, upload a zip that extracts into staging, and
import a single markdown file (agent infers chapter vs character).

src/Novelly.Api/Program.cs

@@ -68,6 +68,12 @@ using (var scope = app.Services.CreateScope())
 
     await ServiceUser.EnsureSeededAsync(db, builder.Configuration[ServiceApiKeyAuthenticationHandler.ConfigurationKey], app.Logger);
     await ActivityBackfill.RunAsync(db, app.Logger);
+
+    var importRoot = builder.Configuration.GetSection(ImportOptions.SectionName)[nameof(ImportOptions.RootPath)];
+    if (!string.IsNullOrWhiteSpace(importRoot))
+    {
+        Directory.CreateDirectory(importRoot);
+    }
 }
 
 app.UseSerilogRequestLogging();