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

resources/views/about.blade.php

@@ -0,0 +1,9 @@
+@extends('master')
+@section('title')About « @stop
+
+@section('content')
+    <h2>About</h2>
+    <div class="e-content">
+        {!! $about !!}
+    </div>
+@stop