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/components/Editor/EditorCore.tsx

@@ -0,0 +1,74 @@
+import { useEditor, EditorContent } from '@tiptap/react'
+import StarterKit from '@tiptap/starter-kit'
+import Underline from '@tiptap/extension-underline'
+import TextAlign from '@tiptap/extension-text-align'
+import Placeholder from '@tiptap/extension-placeholder'
+import CharacterCount from '@tiptap/extension-character-count'
+import { useEffect } from 'react'
+import { Toolbar } from '../Toolbar/Toolbar'
+
+export interface EditorChange {
+  content: string // Tiptap JSON, stringified
+  content_text: string // flattened plain text for the LLM
+  word_count: number
+}
+
+interface Props {
+  // Changing docId reloads the editor with that document's content.
+  docId: string
+  initialContent: string
+  onChange: (change: EditorChange) => void
+}
+
+// parseDoc turns the stored content string into a Tiptap doc node, tolerating
+// the DB's '{}' default and any malformed value by falling back to empty.
+function parseDoc(raw: string): object | undefined {
+  if (!raw) return undefined
+  try {
+    const parsed = JSON.parse(raw)
+    if (parsed && typeof parsed === 'object' && parsed.type === 'doc') return parsed
+  } catch {
+    /* fall through to empty */
+  }
+  return undefined
+}
+
+// EditorCore is the Tiptap instance: StarterKit formatting plus underline, text
+// alignment, a placeholder, and character counting (words feed the StatusBar).
+export function EditorCore({ docId, initialContent, onChange }: Props) {
+  const editor = useEditor({
+    extensions: [
+      StarterKit,
+      Underline,
+      TextAlign.configure({ types: ['heading', 'paragraph'] }),
+      Placeholder.configure({ placeholder: 'Start writing…' }),
+      CharacterCount,
+    ],
+    content: parseDoc(initialContent),
+    editorProps: {
+      attributes: { class: 'petal-prose focus:outline-none' },
+    },
+    onUpdate: ({ editor }) => {
+      onChange({
+        content: JSON.stringify(editor.getJSON()),
+        content_text: editor.getText(),
+        word_count: editor.storage.characterCount.words(),
+      })
+    },
+  })
+
+  // When the selected document changes, swap in its content without emitting an
+  // update (false) so loading a doc doesn't trigger a spurious save.
+  useEffect(() => {
+    if (!editor) return
+    editor.commands.setContent(parseDoc(initialContent) ?? '', false)
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [docId, editor])
+
+  return (
+    <div className="flex flex-1 flex-col">
+      <Toolbar editor={editor} />
+      <EditorContent editor={editor} className="flex-1" />
+    </div>
+  )
+}