Fix New Document button and make editor full-screen

- Replace prompt() with inline title form (button → input → Create/Cancel)
- Editor view: position:fixed inset:0 z-index:200 so it covers full screen
- Docs editor toolbar moved into CSS (was duplicated in styles)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/index.html

@@ -133,6 +133,11 @@
         <div class="docs-toolbar">
           <button id="btn-new-doc" class="docs-new-btn">+ New Document</button>
         </div>
+        <form id="docs-new-form" class="docs-new-form" hidden>
+          <input id="docs-new-title" class="docs-new-input" type="text" placeholder="Document title…" maxlength="120" autocomplete="off">
+          <button type="submit" class="docs-new-btn">Create</button>
+          <button type="button" id="btn-docs-new-cancel" class="docs-cancel-btn">Cancel</button>
+        </form>
         <div id="docs-list"></div>
         <p id="docs-empty" class="hint" hidden>No documents yet — tap + New Document to start writing!</p>
       </div>