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/document.gohtml

@@ -1,9 +1,23 @@
 {{ define "document.gohtml" }}{{ template "base" . }}{{ end }}
 
 {{ define "document_content" }}
-<section class="workspace-shell">
+<section class="workspace-shell workspace-shell--document">
   {{ template "browser" .Browser }}
   <article class="document-shell" data-document-path="{{ .Path }}" data-document-hash="{{ .Hash }}">
+    <nav class="breadcrumbs" aria-label="Breadcrumb">
+      <ol>
+        {{ $lastIdx := sub (len .Breadcrumbs) 1 }}
+        {{ range $i, $crumb := .Breadcrumbs }}
+          <li>
+            {{ if eq $i $lastIdx }}
+              <span aria-current="page">{{ $crumb.Name }}</span>
+            {{ else }}
+              <a href="{{ $crumb.URL }}">{{ $crumb.Name }}</a>
+            {{ end }}
+          </li>
+        {{ end }}
+      </ol>
+    </nav>
     <div class="document-meta">
       <h1>{{ .Title }}</h1>
       <dl class="meta-grid">
@@ -40,17 +54,22 @@
 {{ define "browser" }}
 <nav class="miller-browser" aria-label="Documents">
   {{ range .Columns }}
-    <section class="miller-column" aria-label="{{ .Title }}">
-      <h2>{{ .Title }}</h2>
+    <section class="miller-column {{ if eq .Title "Content" }}miller-column--root{{ end }}" aria-label="{{ .Title }}">
+      <h2 title="{{ .Title }}">
+        {{ if eq .Title "Content" }}
+          <span class="browser-icon browser-icon--root" aria-hidden="true"></span>
+        {{ end }}
+        <span class="miller-column-title-text">{{ .Title }}</span>
+      </h2>
       <ul>
         {{ range .Items }}
           <li>
-            <a class="{{ if .Active }}is-active{{ end }} {{ if .IsFolder }}is-folder{{ end }}" href="{{ .URL }}">
+            <a class="{{ if .Active }}is-active{{ end }} {{ if .IsFolder }}is-folder{{ end }}" href="{{ .URL }}" title="{{ .Name }}">
               <span class="browser-item-label">
-                <span class="browser-icon {{ if .IsFolder }}browser-icon--folder{{ else }}browser-icon--file{{ end }}" aria-hidden="true"></span>
-                <span>{{ .Name }}</span>
+                <span class="browser-icon {{ if .IsFolder }}browser-icon--folder{{ else }}browser-icon--page{{ end }}" aria-hidden="true"></span>
+                <span class="browser-item-name">{{ .Name }}</span>
               </span>
-              {{ if .IsFolder }}<span aria-hidden="true">›</span>{{ end }}
+              {{ if .IsFolder }}<span class="browser-item-chevron" aria-hidden="true">›</span>{{ end }}
             </a>
           </li>
         {{ end }}