feat: miller column browser, offline cache, search, breadcrumbs

- Dynamic miller column sizing with flexbox layout
- Root column (160px), middle slices (48px), active column (flex)
- Auto-scroll browser to rightmost column on navigation
- Offline indicator UI and IndexedDB cache integration
- /api/documents endpoint for client-side document caching
- Breadcrumb navigation in document content area
- FTS5 search with SQLite virtual table
- Client-side Mermaid and KaTeX rendering via CDN
- Deep sample content (advanced-topics/raft-deep-dive)
- Border removal (only search button keeps radius)
- Full viewport layout with proper borders between sidebar/content

apps/server/internal/httpserver/templates/search.gohtml

@@ -0,0 +1,26 @@
+{{ define "search.gohtml" }}{{ template "base" . }}{{ end }}
+
+{{ define "search_content" }}
+<section class="workspace-shell workspace-shell--empty">
+  <section class="search-panel">
+    <p class="eyebrow">Search Results</p>
+    <h1>{{ .Query }}</h1>
+    <p class="lede">{{ len .Results }} document{{ if ne (len .Results) 1 }}s{{ end }} found</p>
+
+    {{ if .Results }}
+      <ul class="search-results">
+        {{ range .Results }}
+          <li>
+            <a href="/docs/{{ trimMd .Path }}">
+              <span class="search-result-title">{{ .Title }}</span>
+              <span class="search-result-path">{{ .Path }}</span>
+            </a>
+          </li>
+        {{ end }}
+      </ul>
+    {{ else }}
+      <p>No documents found matching your search.</p>
+    {{ end }}
+  </section>
+</section>
+{{ end }}