Hide inserted estimates from client list; redirect anon to /signin

Estimates with status Inserted (provider hasn't worked on them yet)
were showing up in the client's "Mes devis à valider" list. The
asclient endpoint now requires ProviderValidationDate to be set, so
only estimates the provider has actually established and submitted
are visible to the client. The asprovider endpoint is unchanged
(providers still need to see incoming unprocessed requests).

Also fix the anonymous-access redirect on Yavsc.Org: the application
cookie's LoginPath defaulted to /Account/Login, which has no
controller. Anonymous hits to a restricted page now redirect to the
real /signin endpoint (with /signout and /Account/AccessDenied set
to match the existing controller routes).

Co-Authored-By: Claude Code <noreply@anthropic.com>

src/Yavsc.Org/Extensions/HostingExtensions.cs

@@ -215,6 +215,18 @@ public static class HostingExtensions
 
         services.AddScoped<IUserClaimsPrincipalFactory<ApplicationUser>, UserClaimsPrincipalFactory<ApplicationUser, IdentityRole>>();
 
+        // The default application cookie LoginPath is "/Account/Login", which
+        // has no controller here — anonymous access to a restricted page must
+        // redirect to the actual sign-in endpoint instead. The paths mirror
+        // the route attributes on AccountController (Constants.SigninPath etc.,
+        // which carry a "~/" prefix that the cookie middleware does not want).
+        services.ConfigureApplicationCookie(options =>
+        {
+            options.LoginPath = "/signin";
+            options.LogoutPath = "/signout";
+            options.AccessDeniedPath = "/Account/AccessDenied";
+        });
+
         // Dev-only: Chromium rejects SameSite=None without Secure on http://
         // (e.g. http://localhost:5000). The default Identity cookie policy
         // sets SameSite=None, which is invalid without Secure. Force Lax in