feat: RCT inline abbreviation tooltip on verdict legend strip (v2.2.1)

- Add abbrs field to Established verdict taxonomy item
- Add peptide_starter_render_desc() helper — builds safe HTML from
  esc_html/esc_attr components; replaces abbr terms with <abbr> tap-targets
- Update front-page.php description output to use render_desc()
- Add assets/js/abbr-tooltip.js — popover open/close, outside-click
  dismissal, keyboard accessibility (Enter/Space/Escape), ARIA attrs
- Enqueue abbr-tooltip.js on is_front_page() only
- Add .pr-abbr and .pr-abbr-popover CSS with dashed underline affordance,
  fade-in animation, dark-mode-safe surface variables
- Fix PEPTIDE_STARTER_VERSION drift: 2.0.0-alpha.3 → 2.2.1

Routing note: this is a theme change (not PR Core). Term 'RCT' is scoped
to the verdict legend strip only; monograph bodies are unaffected.

functions.php

@@ -26,7 +26,7 @@ if ( ! defined( 'ABSPATH' ) ) {
 }
 
 // Theme constants.
-define( 'PEPTIDE_STARTER_VERSION', '2.0.0-alpha.3' );
+define( 'PEPTIDE_STARTER_VERSION', '2.2.1' );
 define( 'PEPTIDE_STARTER_DIR', get_template_directory() );
 define( 'PEPTIDE_STARTER_URI', get_template_directory_uri() );
 
@@ -88,6 +88,11 @@ function peptide_starter_scripts() {
 	wp_enqueue_script( 'peptide-starter-theme', PEPTIDE_STARTER_URI . '/assets/js/theme.js', array(), PEPTIDE_STARTER_VERSION, true );
 	wp_enqueue_script( 'peptide-starter-settings-panel', PEPTIDE_STARTER_URI . '/assets/js/settings-panel.js', array(), PEPTIDE_STARTER_VERSION, true );
 
+	// Abbreviation popovers — only needed on the front page verdict legend strip.
+	if ( is_front_page() ) {
+		wp_enqueue_script( 'peptide-starter-abbr-tooltip', PEPTIDE_STARTER_URI . '/assets/js/abbr-tooltip.js', array(), PEPTIDE_STARTER_VERSION, true );
+	}
+
 	wp_localize_script(
 		'peptide-starter-theme',
 		'peptideStarterData',