Add quick switcher and fix directory refresh races

- Ctrl+P quick switcher with fuzzy matching on note titles and folders; empty input lists
  recent notes with the previous note first; creates the note (and folders) when no note
  has that name; also reachable from the mobile top bar
- Track recently opened notes, following renames and moves
- Serialize directory refreshes and discard responses that raced with local edits; a stale
  response could drop an optimistically added note, and debounced callers could wait
  forever, leaving the workspace startup unfinished
- Wait for a pending note creation before renaming it
- Focus the editor after opening a note from the switcher or search

web/src/app/fuzzy.ts

@@ -0,0 +1,55 @@
+// 快速切换的模糊匹配。目标形如"目录/标题"，空白分隔的每个词都要命中；
+// 连续命中标题 > 连续命中目录 > 按顺序零散命中（如用首字母找笔记）
+
+export interface FuzzyMatch {
+  score: number
+  // 命中字符在目标中的下标，用于高亮
+  positions: number[]
+}
+
+const BOUNDARY = new Set(['/', ' ', '-', '_', '.'])
+
+function isBoundary(target: string, i: number): boolean {
+  return i === 0 || BOUNDARY.has(target[i - 1])
+}
+
+function matchTerm(term: string, target: string, lower: string, titleStart: number): FuzzyMatch | null {
+  // 取最后一处连续命中：标题在末尾，优先落在标题上
+  const at = lower.lastIndexOf(term)
+  if (at >= 0) {
+    let score = at >= titleStart ? 100 : 50
+    if (at === titleStart) score += 30
+    else if (isBoundary(target, at)) score += 10
+    return { score, positions: Array.from(term, (_, k) => at + k) }
+  }
+  const positions: number[] = []
+  let from = 0
+  for (const ch of term) {
+    const i = lower.indexOf(ch, from)
+    if (i < 0) return null
+    positions.push(i)
+    from = i + 1
+  }
+  // 越分散得分越低，命中词首的字符加分
+  const spread = positions[positions.length - 1] - positions[0] + 1 - positions.length
+  const boundaries = positions.filter((i) => isBoundary(target, i)).length
+  return { score: Math.max(1, 20 - spread + boundaries * 3), positions }
+}
+
+/** titleStart 为标题在 target 中的起始下标；不匹配时返回 null */
+export function fuzzyMatch(query: string, target: string, titleStart: number): FuzzyMatch | null {
+  const terms = query.toLowerCase().split(/\s+/).filter(Boolean)
+  if (!terms.length) return null
+  const lower = target.toLowerCase()
+  let score = 0
+  const positions = new Set<number>()
+  for (const term of terms) {
+    const m = matchTerm(term, target, lower, titleStart)
+    if (!m) return null
+    score += m.score
+    m.positions.forEach((p) => positions.add(p))
+  }
+  // 标题与输入完全一致时排在最前
+  if (lower.slice(titleStart) === query.trim().toLowerCase()) score += 1000
+  return { score, positions: [...positions].sort((a, b) => a - b) }
+}