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/editorKit.jsx

@@ -0,0 +1,64 @@
+// Shared form controls for block editors, styled with the existing admin design
+// system (.field-label / .input / .select). Every block's editor is a
+// ({ props, onChange }) component; these keep the seven of them consistent and
+// short. onChange always receives the full next props object.
+
+export function Field({ label, hint, children }) {
+  return (
+    <label style={{ display: 'block' }}>
+      <span className="field-label">{label}</span>
+      {children}
+      {hint && (
+        <span className="sans dim" style={{ display: 'block', fontSize: '0.78rem', marginTop: 4 }}>
+          {hint}
+        </span>
+      )}
+    </label>
+  )
+}
+
+export function TextField({ label, hint, value, onChange, placeholder, maxLength }) {
+  return (
+    <Field label={label} hint={hint}>
+      <input
+        type="text"
+        className="input"
+        value={value ?? ''}
+        placeholder={placeholder}
+        maxLength={maxLength}
+        onChange={(e) => onChange(e.target.value)}
+      />
+    </Field>
+  )
+}
+
+export function TextAreaField({ label, hint, value, onChange, placeholder, rows = 4, maxLength }) {
+  return (
+    <Field label={label} hint={hint}>
+      <textarea
+        className="input"
+        rows={rows}
+        value={value ?? ''}
+        placeholder={placeholder}
+        maxLength={maxLength}
+        onChange={(e) => onChange(e.target.value)}
+        style={{ resize: 'vertical', fontFamily: 'inherit' }}
+      />
+    </Field>
+  )
+}
+
+// options: array of [value, label] tuples.
+export function SelectField({ label, hint, value, onChange, options }) {
+  return (
+    <Field label={label} hint={hint}>
+      <select className="select" value={value ?? ''} onChange={(e) => onChange(e.target.value)}>
+        {options.map(([v, l]) => (
+          <option key={v} value={v}>
+            {l}
+          </option>
+        ))}
+      </select>
+    </Field>
+  )
+}