feat(18-01): chi v5 dependency, go:embed static assets, HTML layout and overview templates

- Add chi v5.2.5 to go.mod
- Vendor htmx v2.0.4 minified JS in pkg/web/static/
- Create go:embed directives for static/ and templates/
- Create layout.html with nav bar and Tailwind CDN
- Create overview.html with stat cards and findings table

pkg/web/static/style.css

@@ -0,0 +1,39 @@
+/* KeyHunter Dashboard — custom overrides (Tailwind CDN handles utility classes) */
+
+body {
+    font-family: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont,
+        "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
+}
+
+/* Stat card styling */
+.stat-card {
+    border-radius: 0.5rem;
+    padding: 1.5rem;
+    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
+}
+
+/* Findings table */
+.findings-table {
+    width: 100%;
+    border-collapse: collapse;
+}
+.findings-table th,
+.findings-table td {
+    padding: 0.75rem 1rem;
+    text-align: left;
+    border-bottom: 1px solid #e5e7eb;
+}
+.findings-table th {
+    font-weight: 600;
+    color: #374151;
+    background-color: #f9fafb;
+}
+.findings-table tr:hover {
+    background-color: #f3f4f6;
+}
+
+/* Navigation active link */
+.nav-link-active {
+    border-bottom: 2px solid #3b82f6;
+    color: #3b82f6;
+}