ux: move banner from Create-Note page to About page (side-by-side intro)

The banner image was the first thing under the page title on the
Create-Note page — taking significant vertical space before the user
saw the textarea. The Create-Note page is for *doing*, not for
*reading-about*.

CHANGES
- Banner removed from wp_notes_page_callback() — Create-Note page
  now opens straight into the form.
- Banner added to the top of the About page in a new side-by-side
  row: image on the left capped at 320px wide (not full-bleed), and
  a short intro paragraph + "Go to WP Notes →" CTA on the right.
  Stacks vertically on narrow screens via flex-wrap.
- The side-by-side block lives in its own .wp-notes-about-intro
  container so it doesn't tangle with the rest of the About page's
  pre-existing nested toggles (those are still on the Tier 2 list).
- .wp-notes-header-banner / .wp-notes-banner-img CSS removed from
  wp-notes-styles.php — no longer referenced anywhere.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,21 @@ Format: [Keep a Changelog 1.1.0](https://keepachangelog.com/en/1.1.0/) — versi
 
 ## [Unreleased]
 
+### Changed — Banner moved to About page (side-by-side intro)
+- **Banner image removed from the Create-Note page.** It was the
+  first thing under the page title and took up significant vertical
+  space before the user even saw the textarea. The Create-Note page
+  is for *doing*, not for *reading-about*.
+- **Banner added to the top of the About page** in a new
+  side-by-side row: banner image on the left (capped at 320px wide,
+  not full-bleed), and a short intro paragraph + "Go to WP Notes →"
+  CTA on the right. Stacks vertically on narrow screens via
+  `flex-wrap`. Lives inside its own `.wp-notes-about-intro` block so
+  it doesn't interact with the rest of the About page's nested
+  toggles.
+- **`.wp-notes-header-banner` / `.wp-notes-banner-img` CSS removed**
+  from `wp-notes-styles.php` — no longer used.
+
 ### Changed — Tier 1 UX cleanup
 Single pass through `wp_notes_page_callback()` to remove the layout
 debt that had built up over previous releases. Functionality is