fix: address QA review findings

1. Typography: install @tailwindcss/typography and add to plugins so prose
   classes render correctly in article/about/legal templates.

2. Callout block: fix icon branches to match CalloutBlock.ICON_CHOICES
   (info/warning/trophy/tip). Previous template branched on error/success
   which are unreachable; info fell through to else silently.

3. Nav newsletter feedback: remove 'hidden' class from desktop nav
   data-newsletter-message element. JS sets textContent only; hidden
   class prevented message from ever being visible.

4. Popular Articles sidebar: add numbered Popular Articles widget to home
   page sidebar matching wireframe, using latest_articles context with
   alternating cyan/pink number accents and read_time_mins.

Rebuild CSS: typography plugin grows output from 24KB to 47KB.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

theme/static_src/package.json

@@ -7,6 +7,7 @@
     "dev": "tailwindcss -i ./src/input.css -o ../static/css/styles.css --watch"
   },
   "devDependencies": {
+    "@tailwindcss/typography": "^0.5.19",
     "tailwindcss": "^3.4.17"
   }
 }