feat: v0.11.0 VS Code-like explorer, markdown preview, search in files

- Explorer: context menus, multi-select, inline rename/new, drag to move
  or copy, desktop drag-and-drop uploads (folders too), cut/copy/paste,
  duplicate, download, delete to a 7-day trash with Undo. Server side in
  libexec/devdesk-fsops.sh with bats tests. Closes #54
- Markdown preview in a shadow root: headings with anchors and outline,
  highlighted code with copy, callouts, task lists, front matter, links
  that open files, live split view. Editor status bar, multi-cursor,
  closeBrackets, Ctrl+G, tab menus and reordering. Closes #55
- Search in files (Ctrl+Shift+F) via git grep / grep. Closes #56
- Fix: nested $(...) path checks now fail hard (set -e does not reach
  them; an escape created /x in testing); newest folder listing wins;
  sessionAction returns the reply JSON.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WHRLCCdXYm41Qx5kNhehaP

web/index.template.html

@@ -109,8 +109,17 @@
         <div class="dd-explorer-views" role="tablist">
           <button type="button" role="tab" data-files-view="explorer" aria-selected="true">Explorer</button>
           <button type="button" role="tab" data-files-view="changes" aria-selected="false">Changes <span class="dd-files-count"></span></button>
+          <button type="button" role="tab" data-files-view="search" aria-selected="false" title="Search in files (Ctrl+Shift+F)">Search</button>
+          <span class="dd-explorer-actions">
+            <button type="button" class="dd-icon-btn" data-explorer-act="new-file" title="New file" aria-label="New file">🗋</button>
+            <button type="button" class="dd-icon-btn" data-explorer-act="new-folder" title="New folder" aria-label="New folder">🗀</button>
+            <button type="button" class="dd-icon-btn" data-explorer-act="upload" title="Upload files (or drop them on a folder)" aria-label="Upload files">⇪</button>
+            <button type="button" class="dd-icon-btn" data-explorer-act="collapse" title="Collapse all folders" aria-label="Collapse all folders">⊟</button>
+          </span>
         </div>
-        <div class="dd-explorer-body" role="tree" aria-label="Files"></div>
+        <div class="dd-explorer-body" role="tree" aria-label="Files" aria-multiselectable="true"></div>
+        <div class="dd-upload-bar" hidden><span class="dd-upload-text"></span><span class="dd-upload-meter"><span class="dd-upload-fill"></span></span></div>
+        <input type="file" class="dd-upload-input" multiple hidden>
       </div>
       <div class="dd-editor-area"></div>
     </div>