Editor: font-size presets + image insert/export support

Two editor features that were in flight alongside the sound work:
- FontSize TipTap extension (rides on textStyle) with Small/Normal/Large/
  Title presets in the toolbar; StatusBar + CSS support
- Image handling: internal/images handler, upload route + config, client
  API, EditorCore wiring, and md/html/docx export support for images

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

web/src/api/client.ts

@@ -182,6 +182,21 @@ export const api = {
   // highlighted snippet. Empty query returns []. Encodes the term for the URL.
   search: (q: string) => req<SearchResult[]>(`/search?q=${encodeURIComponent(q)}`),
 
+  // Image upload: posts a single image file as multipart form data and returns
+  // its served URL (e.g. /api/images/<hash>.png). Stored on disk by the binary,
+  // so the document JSON keeps a small URL reference instead of inlined base64.
+  // Doesn't go through req() because the body is FormData, not JSON.
+  uploadImage: async (file: File): Promise<{ url: string }> => {
+    const form = new FormData()
+    form.append('image', file)
+    const res = await fetch('/api/images', { method: 'POST', body: form })
+    if (!res.ok) {
+      const detail = await res.text().catch(() => '')
+      throw new Error(`${res.status} ${res.statusText}${detail ? `: ${detail}` : ''}`)
+    }
+    return res.json() as Promise<{ url: string }>
+  },
+
   // Tags. listTags returns the roster with per-tag document counts; createTag is
   // idempotent on name (returns the existing tag if it already exists);
   // updateTag recolors/renames; deleteTag removes it (assignments cascade).