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/Template.php

@@ -0,0 +1,100 @@
+<?php
+/*
+ * Small explicit template renderer.
+ *
+ * Templates use escaped {{name}} placeholders and raw {{{name}}} placeholders.
+ * Values are provided as an array, so templates do not depend on globals.
+ */
+
+final class RacketSandboxTemplate
+{
+    const DATA_DELIMITER = "\n===\n";
+
+    public static function renderFile($template, $values)
+    {
+        $parts = self::readFile($template);
+
+        return self::renderString($parts['html'], $values);
+    }
+
+    public static function dataFile($template)
+    {
+        $parts = self::readFile($template);
+        $json = trim($parts['data']);
+
+        if ($json === '') {
+            return array();
+        }
+
+        $data = json_decode($json, true);
+
+        if (!is_array($data)) {
+            throw new RuntimeException('Template data is invalid JSON: ' . $template);
+        }
+
+        return $data;
+    }
+
+    public static function translationsFile($template)
+    {
+        $data = self::dataFile($template);
+        $translations = $data['translations'] ?? array();
+
+        if (!is_array($translations)) {
+            throw new RuntimeException('Template translations must be an object: ' . $template);
+        }
+
+        return $translations;
+    }
+
+    public static function renderString($source, $values)
+    {
+        $source = preg_replace_callback('/\{\{\{\s*([A-Za-z0-9_.-]+)\s*\}\}\}/', function ($match) use ($values) {
+            return self::value($values, $match[1]);
+        }, $source);
+
+        return preg_replace_callback('/\{\{\s*([A-Za-z0-9_.-]+)\s*\}\}/', function ($match) use ($values) {
+            return self::escape(self::value($values, $match[1]));
+        }, $source);
+    }
+
+    public static function escape($value)
+    {
+        return htmlspecialchars((string)$value, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');
+    }
+
+    private static function value($values, $name)
+    {
+        if (!is_array($values) || !array_key_exists($name, $values)) {
+            return '';
+        }
+
+        return (string)$values[$name];
+    }
+
+    private static function readFile($template)
+    {
+        $file = __DIR__ . '/views/' . ltrim((string)$template, '/');
+
+        if (!is_file($file)) {
+            throw new RuntimeException('Template not found: ' . $template);
+        }
+
+        $source = file_get_contents($file);
+
+        if ($source === false) {
+            throw new RuntimeException('Template could not be read: ' . $template);
+        }
+
+        if (strpos($source, "===\n") === 0) {
+            $chunks = array('', substr($source, 4));
+        } else {
+            $chunks = explode(self::DATA_DELIMITER, $source, 2);
+        }
+
+        return array(
+            'html' => $chunks[0],
+            'data' => $chunks[1] ?? '',
+        );
+    }
+}