feat: v4.6.0 — AI assistant, collaboration, knowledge base, and 15 more features

- AI Assistant plugin: multi-provider chat (OpenAI/Anthropic/Ollama/LM Studio),
  summarize/improve/translate commands, proofread via ai:analyze; calls
  proxied through main so API keys stay out of the renderer
- Collaboration plugin: anchor-based comments in .comments/ sidecars with
  drift detection and F8 navigation
- Local knowledge base: [[wiki-links]] with click-to-create + Backlinks panel
- Crash recovery: debounced session snapshots with restore prompt on launch
- Version history: pre-save snapshots, History panel with restore/diff/delete
- Real PDF encryption: swap pdf-lib for @cantoo/pdf-lib (probe-driven UI)
- XLSX export (native workbooks via JSZip), ODT headers/footers + page size
- Offline KaTeX (bundled CSS+fonts), local-first PlantUML rendering
- Editor: vim mode toggle, snippet Tab-expansion, zen word-goal setter,
  writing heatmap, writing-studio panels wired with rail icons
- Quick Note global scratchpad (Ctrl+Alt+Q), markdownconverter:// deep links,
  REPL first-run confirmation
- Fix: Ctrl+Shift+P collision, pandoc converter availability check, CLI
  dangling --css/--reference-doc flags, dead converter button

8 new test suites; 613 tests green; lint clean

src/index.html

@@ -22,6 +22,8 @@
     <link rel="stylesheet" href="styles-welcome.css" />
     <link rel="stylesheet" href="styles-zen.css" />
     <link rel="stylesheet" href="../node_modules/highlight.js/styles/default.css" />
+    <!-- KaTeX math rendering — bundled locally (fonts included) for offline use -->
+    <link rel="stylesheet" href="../assets/katex/katex.min.css" />
   </head>
   <body>
     <!-- Skip link for keyboard navigation -->
@@ -1256,11 +1258,9 @@
               <div class="converter-options pandoc-options hidden">
                 <div class="export-section">
                   <small
-                    >Pandoc conversions can use advanced export options from the Export menu.</small
+                    >Pandoc conversions use the same engine as the Export menu. For advanced options
+                    (metadata, TOC, templates, bibliography), use File → Export instead.</small
                   >
-                  <button id="pandoc-show-export-options" type="button">
-                    Open Export Options Dialog...
-                  </button>
                 </div>
               </div>
             </div>
@@ -2506,6 +2506,38 @@
                 <line x1="3" y1="18" x2="3.01" y2="18" />
               </svg>
             </button>
+            <!-- Backlinks: local knowledge-base panel (wiki-link graph) -->
+            <button class="sidebar-icon" data-panel="backlinks" title="Backlinks">
+              <svg
+                width="20"
+                height="20"
+                viewBox="0 0 24 24"
+                fill="none"
+                stroke="currentColor"
+                stroke-width="2"
+                stroke-linecap="round"
+                stroke-linejoin="round"
+              >
+                <path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71" />
+                <path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71" />
+              </svg>
+            </button>
+            <!-- History: local version history (snapshots before saves) -->
+            <button class="sidebar-icon" data-panel="history" title="Version History">
+              <svg
+                width="20"
+                height="20"
+                viewBox="0 0 24 24"
+                fill="none"
+                stroke="currentColor"
+                stroke-width="2"
+                stroke-linecap="round"
+                stroke-linejoin="round"
+              >
+                <circle cx="12" cy="12" r="10" />
+                <polyline points="12 6 12 12 16 14" />
+              </svg>
+            </button>
           </div>
           <div class="sidebar-panel" id="sidebar-panel">
             <div class="sidebar-panel-header">