Add full-text search

- Index notes in a separate, rebuildable SQLite database (index.db) using FTS5 trigram,
  synced from watcher snapshots so external edits are picked up; terms under 3 characters
  fall back to LIKE
- GET /api/v1/search?q= returns matching notes with the first matching line and a snippet;
  path matches rank first
- Sidebar search panel (Ctrl+Shift+F) with highlighted terms and keyboard navigation;
  opening a result jumps to and selects the match
- Restore scroll position on tab switch with scroll snapshots; restoring scrollTop drifted
  by a few lines after line heights were re-estimated

web/src/app/EditorPane.vue

@@ -1,16 +1,23 @@
 <script setup lang="ts">
-import { EditorState } from '@codemirror/state'
+import { EditorState, type StateEffect, type Text } from '@codemirror/state'
 import type { EditorView } from '@codemirror/view'
 import { computed, onBeforeUnmount, onMounted, ref, watch } from 'vue'
 import { createEditorView } from '../editor'
-import { activeTab, attachView, editorStateOf, noteRefOf, storeViewState, ws } from './workspace'
+import { activeTab, attachView, editorStateOf, noteRefOf, revealPending, storeViewState, ws } from './workspace'
 
 const host = ref<HTMLElement>()
 const tab = computed(activeTab)
 let view: EditorView
-// 当前显示的笔记（以身份对象标识，重命名后不变）及各笔记的滚动位置
+// 当前显示的笔记（以身份对象标识，重命名后不变）及各笔记的滚动位置。
+// 优先用滚动快照（锚定文档位置）：重设状态后视口外的行高会重新估算，单靠 scrollTop 会偏移几行；
+// 快照只对同一文档有效，笔记在后台被外部修改时退回 scrollTop
+interface ScrollPosition {
+  doc: Text
+  snapshot: StateEffect<unknown>
+  top: number
+}
 let shown: { path: string } | undefined
-const scrollTops = new WeakMap<object, number>()
+const scrollPositions = new WeakMap<object, ScrollPosition>()
 
 function show() {
   const path = ws.active
@@ -18,7 +25,7 @@ function show() {
   const state = path ? editorStateOf(path) : undefined
   if (shown && shown !== ref) {
     storeViewState(shown.path, view.state)
-    scrollTops.set(shown, view.scrollDOM.scrollTop)
+    scrollPositions.set(shown, { doc: view.state.doc, snapshot: view.scrollSnapshot(), top: view.scrollDOM.scrollTop })
   }
   if (!ref || !state) {
     shown = undefined
@@ -27,8 +34,13 @@ function show() {
   // 切换笔记，或该笔记的状态在别处被整体替换（如恢复草稿）时才重设
   if (shown !== ref || state.doc !== view.state.doc) {
     view.setState(state)
-    const top = scrollTops.get(ref) ?? 0
-    requestAnimationFrame(() => (view.scrollDOM.scrollTop = top))
+    const pos = scrollPositions.get(ref)
+    // 等一帧：v-show 在此回调之后才取消 display:none，隐藏状态下无法滚动和聚焦
+    requestAnimationFrame(() => {
+      if (shown !== ref || revealPending(view, ref.path)) return
+      if (pos?.doc === view.state.doc) view.dispatch({ effects: pos.snapshot })
+      else view.scrollDOM.scrollTop = pos?.top ?? 0
+    })
   }
   shown = ref
 }