v0.3.4: Bug修复+性能优化+文档大纲功能

🔴 Bug修复 (6):
- Sidebar反斜杠正则修复 (Windows路径规范化)
- FileWatcher文件删除后自动恢复监听
- SearchReplace replaceAll防过期匹配位置
- openFolderDialog null结果守卫
- 保存异常时空路径保护
- Markdown绝对路径图片拼接修复

🟡 性能优化:
- Editor切换标签时内容比较，相同跳过replaceAll

🔵 代码质量:
- 创建共享常量模块 src/shared/constants.ts，消除双副本

🎯 新增功能:
- 文档大纲 (Table of Contents) — 侧边栏标题导航

🔧 换行符统一: CRLF → LF

src/renderer/styles/global.css

@@ -1600,3 +1600,107 @@ button:focus-visible,
   background: rgba(255, 180, 0, 0.4);
   outline-color: rgba(255, 180, 0, 0.6);
 }
+
+/* ===== Outline Panel (Table of Contents) ===== */
+
+.sidebar-outline-section {
+  flex-shrink: 0;
+  max-height: 40%;
+  border-top: 1px solid var(--border);
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
+}
+
+.outline-panel {
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
+  min-height: 0;
+}
+
+.outline-header {
+  padding: 8px 12px;
+  font-size: 11px;
+  font-weight: 600;
+  color: var(--text-secondary);
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+  flex-shrink: 0;
+  border-bottom: 1px solid var(--border-light);
+}
+
+.outline-list {
+  flex: 1;
+  overflow-y: auto;
+  padding: 4px 0;
+}
+
+.outline-list::-webkit-scrollbar {
+  width: 4px;
+}
+
+.outline-list::-webkit-scrollbar-thumb {
+  background: var(--text-tertiary);
+  border-radius: 2px;
+}
+
+.outline-item {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  width: 100%;
+  padding: 3px 8px;
+  border: none;
+  background: transparent;
+  color: var(--text-secondary);
+  font-size: 12px;
+  font-family: var(--font-ui);
+  cursor: pointer;
+  text-align: left;
+  transition: all 0.1s ease;
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.outline-item:hover {
+  background: var(--bg-tertiary);
+  color: var(--text);
+}
+
+.outline-item.active {
+  color: var(--primary);
+  background: var(--primary-light);
+}
+
+.outline-item:focus-visible {
+  outline: 2px solid var(--primary);
+  outline-offset: -2px;
+}
+
+.outline-level-dot {
+  width: 4px;
+  height: 4px;
+  border-radius: 50%;
+  background: var(--text-tertiary);
+  flex-shrink: 0;
+}
+
+.outline-item:hover .outline-level-dot,
+.outline-item.active .outline-level-dot {
+  background: var(--primary);
+}
+
+.outline-item-text {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.outline-empty {
+  padding: 13px 12px;
+  font-size: 11px;
+  color: var(--text-tertiary);
+  text-align: center;
+}