feat(phasefinal-web): expand site to a multi-page cluster

Single page grows to nine: custom app development, systems engineering,
hosting, and AI services each get a detail page, plus engagement,
track-record, contact, and privacy. Cross-linked nav and footer on every
page; brand CSS extended in place (still zero external requests, zero JS).

Motivation: an app-store registration review flagged the single-page site
as minimal content. This version is intended to be reverted after approval.

stacks/phasefinal-web/conf/site/index.html

@@ -4,7 +4,7 @@
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <title>Phase Final, Inc. — Systems Engineering Consultancy</title>
-<meta name="description" content="Phase Final, Inc. is a systems engineering consultancy offering systems engineering, infrastructure hosting, and AI services, with a track record in hardware, firmware, and software engineering.">
+<meta name="description" content="Phase Final, Inc. is a systems engineering consultancy offering custom application development, systems engineering, infrastructure hosting, and AI services, with a track record in hardware, firmware, and software engineering.">
 <link rel="icon" href="favicon.svg" type="image/svg+xml">
 <link rel="stylesheet" href="style.css">
 </head>
@@ -26,6 +26,19 @@
   </div>
 </header>
 
+<nav class="site-nav" aria-label="Site">
+  <ul>
+    <li><a aria-current="page" href="/">Home</a></li>
+    <li><a href="/services/software/">Custom App Development</a></li>
+    <li><a href="/services/systems-engineering/">Systems Engineering</a></li>
+    <li><a href="/services/hosting/">Hosting</a></li>
+    <li><a href="/services/ai/">AI Services</a></li>
+    <li><a href="/engagement/">Engagement</a></li>
+    <li><a href="/track-record/">Track Record</a></li>
+    <li><a href="/contact/">Contact</a></li>
+  </ul>
+</nav>
+
 <main>
 
 <section id="services">
@@ -33,15 +46,19 @@
   <div class="section-body">
     <ul class="service-list">
       <li>
-        <h3>Systems Engineering</h3>
+        <h3><a href="/services/software/">Custom Application Development</a></h3>
+        <p>Native mobile, web, and desktop applications built to the client's spec — designed, shipped, and operated by the same team. iOS, Android, backend services, and the release pipeline behind them.</p>
+      </li>
+      <li>
+        <h3><a href="/services/systems-engineering/">Systems Engineering</a></h3>
         <p>Design and integration of complete systems, hardware and software. Requirements, architecture, implementation, and verification are treated as one problem with one owner.</p>
       </li>
       <li>
-        <h3>Infrastructure Hosting</h3>
+        <h3><a href="/services/hosting/">Infrastructure Hosting</a></h3>
         <p>Hosting and operation of client infrastructure. Systems the firm builds can run on infrastructure the firm operates, under the same accountability.</p>
       </li>
       <li>
-        <h3>AI Services &amp; Engineering</h3>
+        <h3><a href="/services/ai/">AI Services &amp; Engineering</a></h3>
         <p>Engineering and operation of AI systems. Model-backed capability is built, integrated, and run as production software, held to the same standard as everything else the firm ships.</p>
       </li>
     </ul>
@@ -52,7 +69,7 @@
   <h2><span class="num">02</span>How we engage</h2>
   <div class="section-body">
     <p>Engagements are fixed-bid or retainer. Fixed-bid where the scope can be specified: a defined deliverable at a defined price. Retainer where the work is continuous: operation, maintenance, and engineering capacity over time.</p>
-    <p class="referral-note">Most new work arrives by referral.</p>
+    <p class="referral-note">Most new work arrives by referral. <a href="/engagement/">How an engagement runs →</a></p>
   </div>
 </section>