Fix login redirect and hide PHP errors on pages

app/include_header.php

@@ -1,4 +1,23 @@
 <?php
+// Output buffering must be active before the first byte of HTML below, so that
+// header() calls made later in the page still work — notably the
+// not-logged-in redirect in include_topbar.php, which runs *after* this file
+// has already emitted <!DOCTYPE html>. Without a buffer that redirect depends
+// entirely on php.ini's output_buffering: it is on for the dev stack but off
+// in production, where every protected page answered 200 with a half-rendered
+// body instead of sending the browser to the login form. session.php starts a
+// buffer for the same reason.
+if (ob_get_level() === 0) {
+    ob_start();
+}
+
+// Never render PHP notices/warnings into the page: they leak absolute server
+// paths to anonymous visitors and corrupt the markup. Errors still reach the
+// server log. This mirrors the policy db_auth.php already applies to the JSON
+// API routes, and keeps the app safe even where php.ini has display_errors on.
+ini_set('display_errors', '0');
+ini_set('log_errors', '1');
+
 // Security headers — emitted before any HTML output.
 header('X-Content-Type-Options: nosniff');
 header('X-Frame-Options: SAMEORIGIN');