Phase 2: document CRUD + auto-save

Backend internal/docs: chi sub-router (list/create/get/update/delete)
mounted at /api/docs, scoped to the local user. Create uses RETURNING;
update is a COALESCE partial-update so rename and full editor save share
one PUT. JSON 404/400 errors; handlers_test.go walks the lifecycle.

Frontend: api/client.ts, useAutoSave (1.5s debounce + saveNow flush
before doc switch), EditorCore (Tiptap StarterKit/Underline/TextAlign/
Placeholder/CharacterCount) + Toolbar, DocList/DocListItem, StatusBar,
and an App.tsx that orchestrates load/select/create/delete with
optimistic sidebar patching. content + content_text + word_count are
emitted together on every edit. .petal-prose styling (Lora body, Nunito
headings).

Verified: tsc clean, vite build, go build, full CRUD smoke test incl.
CJK title round-trip and SPA serve.

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

web/src/hooks/useAutoSave.ts

@@ -0,0 +1,66 @@
+import { useCallback, useEffect, useRef, useState } from 'react'
+import { api, type DocUpdate } from '../api/client'
+
+export type SaveStatus = 'idle' | 'pending' | 'saving' | 'saved' | 'error'
+
+const DEBOUNCE_MS = 1500
+const SAVED_FADE_MS = 3000
+
+// useAutoSave debounces document saves. Call schedule() on every edit; it fires
+// PUT /api/docs/:id 1.5s after the last change. status drives the StatusBar:
+// pending → saving → saved (fades to idle after 3s).
+export function useAutoSave(docId: string | null) {
+  const [status, setStatus] = useState<SaveStatus>('idle')
+
+  const debounceRef = useRef<ReturnType<typeof setTimeout>>(undefined)
+  const fadeRef = useRef<ReturnType<typeof setTimeout>>(undefined)
+  const pendingRef = useRef<DocUpdate | null>(null)
+  // Latest doc id, read inside the timer so a doc switch doesn't save to the old one.
+  const docIdRef = useRef(docId)
+  docIdRef.current = docId
+
+  const flush = useCallback(async () => {
+    const id = docIdRef.current
+    const body = pendingRef.current
+    pendingRef.current = null
+    if (!id || !body) return
+
+    setStatus('saving')
+    try {
+      await api.updateDoc(id, body)
+      setStatus('saved')
+      clearTimeout(fadeRef.current)
+      fadeRef.current = setTimeout(() => setStatus('idle'), SAVED_FADE_MS)
+    } catch (err) {
+      console.error('auto-save failed', err)
+      setStatus('error')
+    }
+  }, [])
+
+  const schedule = useCallback(
+    (update: DocUpdate) => {
+      pendingRef.current = { ...pendingRef.current, ...update }
+      setStatus('pending')
+      clearTimeout(fadeRef.current)
+      clearTimeout(debounceRef.current)
+      debounceRef.current = setTimeout(flush, DEBOUNCE_MS)
+    },
+    [flush],
+  )
+
+  // Save any pending edits immediately (e.g. before switching documents).
+  const saveNow = useCallback(() => {
+    clearTimeout(debounceRef.current)
+    return flush()
+  }, [flush])
+
+  useEffect(
+    () => () => {
+      clearTimeout(debounceRef.current)
+      clearTimeout(fadeRef.current)
+    },
+    [],
+  )
+
+  return { status, schedule, saveNow }
+}