feat(web): render editable tables and make images clickable

- Top-level GFM tables render as an editable widget: click a cell to
  edit its Markdown source, Tab/Enter/arrows to navigate, toolbar to
  insert/delete rows and columns or switch to source
- Structural table edits are isolated undo steps; focus is restored
  after the widget is rebuilt
- Clicking an image moves the cursor to its syntax to reveal the source
- Renderer escapes raw HTML and filters dangerous URL schemes by default

web/src/editor/index.ts

@@ -4,6 +4,7 @@ import { EditorState, Prec, type Extension } from '@codemirror/state'
 import { drawSelection, EditorView, keymap } from '@codemirror/view'
 import { codeBlockHighlight } from './codeblocks'
 import { livePreview, resolveImageUrl } from './livepreview'
+import { tableEditing } from './table'
 import { markdownTheme } from './theme'
 
 export interface EditorOptions {
@@ -26,6 +27,7 @@ export function createEditor(opts: EditorOptions): EditorView {
     markdownTheme,
     livePreview,
     codeBlockHighlight,
+    tableEditing,
     keymap.of([indentWithTab, ...defaultKeymap, ...historyKeymap]),
     EditorView.contentAttributes.of({ spellcheck: 'false', autocapitalize: 'sentences' }),
   ]