Add admin-editable About page

Mirrors the existing Bio singleton pattern: a new `about` table/model,
admin CRUD at /admin/about, and a public page at /about linked from
both the header nav and the admin homepage. Content is wrapped in
.e-content so it lays out correctly within the site's CSS grid.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013bzYwaDD8p3XNDMYKvXKrs

database/factories/AboutFactory.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Database\Factories;
+
+use App\Models\About;
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends Factory<About>
+ */
+class AboutFactory extends Factory
+{
+    /**
+     * Define the model's default state.
+     *
+     * @return array<string, mixed>
+     */
+    public function definition(): array
+    {
+        return [
+            'content' => $this->faker->paragraph,
+        ];
+    }
+}