Set up Rails 8 application foundation

- Generate Rails 8.1 app with PostgreSQL and TailwindCSS
- Add docker-compose.yml (postgres:17) for local database
- Configure database.yml to connect to Dockerized Postgres via env vars
- Add Pages#home root route, application layout, and navbar partial

app/views/pages/home.html.erb

@@ -0,0 +1,23 @@
+<% content_for :title, "Home" %>
+
+<div class="space-y-6">
+  <header class="space-y-2">
+    <h1 class="text-2xl font-bold tracking-tight text-gray-900">
+      Characterization Tool for Git Workflows
+    </h1>
+    <p class="max-w-2xl text-gray-600">
+      Create, manage, and review structured characterizations of Git workflows
+      using a guided, framework-based process.
+    </p>
+  </header>
+
+  <div class="rounded-lg border border-gray-200 bg-white p-6">
+    <h2 class="text-sm font-semibold uppercase tracking-wide text-gray-500">
+      Getting started
+    </h2>
+    <p class="mt-2 text-gray-700">
+      The application foundation is in place. Characterization features will be
+      added in upcoming work.
+    </p>
+  </div>
+</div>