feat: update HTTP handlers and templates for shelf model

templates/index.mustache

@@ -40,10 +40,6 @@
   .group { padding:10px 14px 4px; font-size:11px; letter-spacing:0.04em; color: var(--text-tertiary); }
   .row { display:flex; align-items:center; gap:10px; padding:5px 14px; font-size:13px; }
   .glyph { font-size:15px; color:var(--text-tertiary); width:16px; }
-  .pill { padding:1px 7px; border-radius:var(--radius-md); font-size:11px; }
-  .pill.want { background:var(--bg-info); color:var(--text-info); }
-  .pill.reading { background:var(--bg-warning); color:var(--text-warning); }
-  .pill.read { background:var(--bg-success); color:var(--text-success); }
   .title { flex:1; min-width:0; }
   .muted { color:var(--text-tertiary); }
   .tags { color:var(--text-info); font-size:12px; }
@@ -66,30 +62,22 @@
   <div class="frame">
     <div class="titlebar">
       <span style="font-weight:500;">spine</span>
-      <span class="muted">{{total_books}} books · {{reading_count}} reading</span>
+      <span class="muted">{{total_books}} books · {{shelf_count}} shelves</span>
     </div>
 
-    {{#current_filter}}
     <div class="filter-bar">
-      <a href="/index">Concise view</a>
-    </div>
-    {{/current_filter}}
-    {{^current_filter}}
-    <div class="filter-bar">
-      <a href="/index?filter=all">All books ({{total_books}})</a>
+      <a href="/index"{{^current_shelf}} style="font-weight:600"{{/current_shelf}}>All</a>
+      {{#shelf_nav}}
       &nbsp;·&nbsp;
-      <a href="/index?filter=want">Want list</a>
-      &nbsp;·&nbsp;
-      <a href="/index?filter=read">Read ({{reading_count}})</a>
+      <a href="{{href}}"{{#current}} style="font-weight:600"{{/current}}>{{name}}</a>
+      {{/shelf_nav}}
     </div>
-    {{/current_filter}}
 
     {{#groups}}
     <div class="group">{{label}} · {{count}}</div>
     {{#books}}
     <div class="row{{#selected}} selected{{/selected}}">
       <i class="ti {{format_icon}} glyph" aria-hidden="true"></i>
-      <span class="pill {{status_class}}">{{status_label}}</span>
       <span class="title">{{title}} <span class="muted">· {{author}}</span></span>
       {{#tags_inline}}<span class="tags">{{tags_inline}}</span>{{/tags_inline}}
       {{#rec_via}}<span class="trail">via {{rec_via}}</span>{{/rec_via}}
@@ -106,10 +94,6 @@
     {{/books}}
     {{/groups}}
 
-    {{#summary_groups}}
-    <div class="group"><a href="{{href}}" style="color:var(--text-info);text-decoration:none">{{label}} · {{count}}</a></div>
-    {{/summary_groups}}
-
     {{#minibuffer}}
     <div class="minibuffer">
       <span class="muted">M-x</span>