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.

CHANGELOG.md

@@ -1,5 +1,29 @@
 # Peptide Starter Theme - Changelog
 
+## [2.2.1] - 2026-04-29 — RCT inline abbreviation tooltip
+
+### Added
+
+- `.pr-abbr` tap-target on the term "RCT" in the Established verdict card on
+  the verdict legend strip (homepage). Tapping/clicking opens a small inline
+  popover with the full definition: "Randomized Controlled Trial — the gold
+  standard for clinical evidence." Closes on outside click, Escape key, or
+  focus leaving the element.
+- `assets/js/abbr-tooltip.js` — new JS module (~130 lines) for popover open/
+  close, outside-click dismissal, keyboard accessibility (Enter/Space/Escape),
+  and ARIA attributes (`aria-expanded`, `aria-describedby`, `role="tooltip"`).
+  Enqueued on front page only (`is_front_page()`).
+- `peptide_starter_render_desc( string $text, array $abbrs ): string` helper in
+  `inc/verdict-helpers.php`. Builds safe HTML from `esc_html`/`esc_attr`
+  components; verdict taxonomy items carry an optional `abbrs` map.
+- `.pr-abbr` and `.pr-abbr-popover` CSS in `style.css` — dashed underline
+  affordance, fade-in animation, dark-mode-safe surface variables.
+
+### Fixed
+
+- `PEPTIDE_STARTER_VERSION` constant in `functions.php` was stale at
+  `2.0.0-alpha.3`; realigned to `2.2.1` to match `style.css` Version header.
+
 ## [2.1.8] - 2026-04-28 — Homepage verdict section spacing fix
 
 ### Fixed