Add Wave 1 block renderers + editors (page builder step 3, client half)

Client block registry now carries a renderer, edit form, palette label/icon,
and defaults for all seven Wave 1 blocks (self-registering via
client/src/blocks/types/*): heading, rich_text, image, two_column, cta,
divider, quote.

- BlockRenderer + BlockList render stored blocks via the registry (respect
  `visible`, tolerate unknown types), reading getBlock from ./registry to
  avoid the index -> twoColumn -> BlockRenderer cycle.
- editorKit: shared Field/TextField/TextAreaField/SelectField styled with the
  existing admin form classes; rich_text editor reuses RichTextEditor
  (variant post), image editor reuses the shared uploader.
- two_column editor is a mini per-column canvas (add from the leaf-only
  palette, edit via each block's registry editor, reorder, remove).
- theme.css: public block styles (heading/image alignment/cta/quote/
  two-column responsive grid) + column sub-block editor styles.

Verified: all 11 modules transform cleanly under esbuild. Full visual
verification comes with the builder UI (step 5) + public route (step 6).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/src/blocks/BlockRenderer.jsx

@@ -0,0 +1,26 @@
+// Renders stored blocks via their registry component. Used by the public page
+// route, the draft preview, and (recursively) the two_column block. Kept
+// separate from the registry so both the renderer and the builder can import it.
+// Import the lookup from the registry directly (not ./index) to avoid a cycle:
+// index → types/twoColumn → BlockRenderer. The page route/builder import ./index,
+// which registers every block before anything renders.
+import { getBlock } from './registry.js'
+
+/**
+ * Render one block. A block with `visible === false` renders nothing (admins
+ * hide blocks without deleting them). An unknown type also renders nothing —
+ * server validation prevents storing one, so this only guards a client/server
+ * registry skew rather than crashing the whole page.
+ */
+export default function BlockRenderer({ block }) {
+  if (!block || block.visible === false) return null
+  const def = getBlock(block.type)
+  if (!def || !def.component) return null
+  const Component = def.component
+  return <Component props={block.props || {}} block={block} />
+}
+
+/** Render an ordered array of blocks (array position = display order). */
+export function BlockList({ blocks }) {
+  return (blocks || []).map((block) => <BlockRenderer key={block.id} block={block} />)
+}