Move rendering into private templates

Add an explicit template renderer with HTML views and partials for the app, bootstrap, package, and catalog pages. Move shared reporting setup into config/reporting.php and relocate stylesheet assets under css/.

private/views/app-header.html

@@ -0,0 +1,15 @@
+<header class="page-header">
+<div class="page-titlebar">
+<h1>{{title}}</h1>
+
+<nav class="header-nav" aria-label="{{title}} navigation">
+{{{nav_html}}}
+{{{logout_html}}}
+{{{user_html}}}
+{{{language_html}}}
+</nav>
+</div>
+
+{{{message_html}}}
+{{{error_html}}}
+</header>