ux: Tier 1 cleanup of wp_notes_page_callback — single H1, collapse triple welcome surfaces, footer support link

Single-pass UX cleanup of the main WP Notes admin page. Functionality
unchanged; the page is shorter, has one H1, and stops contradicting
itself.

CHANGES
- Single H1 on the page (was five different H1s).
- Welcome/about content collapsed from THREE on-page surfaces (top
  dismissible notice + nested toggle + Show/Close button row) to one
  single description line linking to the dedicated About page where
  the long copy already lives.
- Two duplicate "Toggle Welcome Section" buttons with the SAME label
  but different targets — both removed.
- Embedded "What's New v3.0.0" changelog block deleted: it was
  hard-coded to v3.0.0 while the plugin reports v3.0.2. The real
  history is in CHANGELOG.md.
- "Buy me a coffee" button moved from page header to page footer —
  promo shouldn't be the first thing under the page title.
- Invalid HTML cleaned up (li outside ul, p wrapping div/ul) by way
  of removing the welcome blob that contained it.
- Dead bulk-action UI removed: per-row checkboxes and "Select all"
  header in both wp_notes_display_notes() and wp_notes_list_table()
  rendered but nothing acted on the selection. Removed with inline
  comments marking the spot for when real bulk-actions land. Edit
  form colspan adjusted to match the new column count.
- ~80 lines of inline style+script for the about-box dismissal
  removed (localStorage tracking, show/hide handlers, two style
  blocks). WordPress's notice notice-info is-dismissible + user-meta
  is the right path if a banner needs to return.
- toggleSection() JS helper removed (no toggles remain).
- Small CSS additions to inc/wp-notes-styles.php for the header
  banner and footer-support link.

ALSO FIXED
- PHP 8.2 deprecation: ${size}px → {$size}px in the dashboard
  list-table render. ${var} interpolation is deprecated since 8.2
  and will hard-error in 9.0.

NET DIFF: wp-notes.php -213 lines, total -111 lines across 4 files
(plus a new CHANGELOG entry). Storage model unchanged.

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

inc/wp-notes-styles.php

@@ -11,6 +11,24 @@ if (!defined('ABSPATH')) {
 function wp_notes_admin_styles() {
     ?>
     <style>
+        /* Header banner image */
+        .wp-notes-header-banner {
+            margin: 16px 0 24px;
+        }
+        .wp-notes-banner-img {
+            display: block;
+            max-width: 1200px;
+            width: 100%;
+            height: auto;
+            border-radius: 4px;
+        }
+
+        /* Footer "buy me a coffee" — lives at the BOTTOM of the page */
+        .wp-notes-footer-support {
+            text-align: center;
+            margin: 32px 0 8px;
+        }
+
         /* Notes List Container */
         .wp-notes-active,
         .wp-notes-completed {