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/api/client.ts

@@ -0,0 +1,51 @@
+// Thin fetch wrappers for the Petal backend. Everything lives under /api, which
+// Vite proxies to the Go server in dev and the binary serves directly in prod.
+
+export interface DocSummary {
+  id: string
+  title: string
+  word_count: number
+  updated_at: string
+}
+
+export interface Document {
+  id: string
+  user_id: string
+  title: string
+  content: string // Tiptap JSON (stringified)
+  content_text: string // flattened plain text
+  word_count: number
+  created_at: string
+  updated_at: string
+}
+
+// Fields the editor sends on auto-save. All optional so a rename can send title
+// alone; the editor sends the full set.
+export interface DocUpdate {
+  title?: string
+  content?: string
+  content_text?: string
+  word_count?: number
+}
+
+async function req<T>(path: string, init?: RequestInit): Promise<T> {
+  const res = await fetch(`/api${path}`, {
+    headers: { 'Content-Type': 'application/json' },
+    ...init,
+  })
+  if (!res.ok) {
+    const detail = await res.text().catch(() => '')
+    throw new Error(`${res.status} ${res.statusText}${detail ? `: ${detail}` : ''}`)
+  }
+  if (res.status === 204) return undefined as T
+  return res.json() as Promise<T>
+}
+
+export const api = {
+  listDocs: () => req<DocSummary[]>('/docs'),
+  createDoc: () => req<Document>('/docs', { method: 'POST' }),
+  getDoc: (id: string) => req<Document>(`/docs/${id}`),
+  updateDoc: (id: string, body: DocUpdate) =>
+    req<Document>(`/docs/${id}`, { method: 'PUT', body: JSON.stringify(body) }),
+  deleteDoc: (id: string) => req<void>(`/docs/${id}`, { method: 'DELETE' }),
+}