Refactor GL period and entry date handling to use BusinessClock for accurate date resolution; add GlAccountCodeValidator for startup validation of configured account codes.

Backend/ERPCore/Program.cs

@@ -77,12 +77,22 @@ builder.Services.AddScoped<IAuthAltService, AuthAltService>();
 // General Ledger service proxy → external GL microservice (docs/12-GENERAL-LEDGER-INTEGRATION.md)
 builder.Services.AddHttpClient<IGeneralLedgerClient, GeneralLedgerClient>(c =>
 {
-    var baseUrl = builder.Configuration["GeneralLedgerService:BaseUrl"]
-        ?? throw new InvalidOperationException("GeneralLedgerService:BaseUrl is not configured.");
+    var baseUrl = builder.Configuration["GeneralLedgerService:BaseUrl"];
+    if (string.IsNullOrWhiteSpace(baseUrl))
+        throw new InvalidOperationException("GeneralLedgerService:BaseUrl is not configured.");
+
+    // GeneralLedgerClient builds *relative* URIs ("journal-entries", "accounts", …), so the base
+    // address must keep its full path — including /api/v1/ — and end in '/'. Without the trailing
+    // slash, Uri resolution replaces the last segment and every call lands on /api/journal-entries.
+    if (!baseUrl.EndsWith('/')) baseUrl += "/";
     c.BaseAddress = new Uri(baseUrl);
 });
 builder.Services.AddScoped<IGeneralLedgerService, GeneralLedgerService>();
 
+// Fail fast on a misconfigured chart of accounts: every Gl*Code in configuration must exist in GL,
+// otherwise the first user to touch that flow eats a 404 mid-transaction.
+builder.Services.AddHostedService<GlAccountCodeValidator>();
+
 // Current-user (audit actor). AuthHex has no sub/nameid → a claims transformation
 // JIT-provisions a local shadow user and injects the local `int` id as `nameid`.
 builder.Services.AddHttpContextAccessor();