fix: align templates with wireframe styling

- Fix article header tag borders: replace broken border-current/20
  (Tailwind can't apply opacity to currentColor) with per-tag border
  colour classes via new get_tag_border_css filter
- Add calendar icon before article date in article header
- Add clock icon before read time in article header and home featured
- Match article card footer to wireframe (remove extra min-read span)
- Add rounded-md to code block matching wireframe

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

apps/blog/models.py

@@ -100,12 +100,24 @@ class TagMetadata(models.Model):
 
     @classmethod
     def get_fallback_css(cls) -> dict[str, str]:
-        return {"bg": "bg-zinc-800 dark:bg-zinc-100", "text": "text-white dark:text-black"}
+        return {
+            "bg": "bg-zinc-800 dark:bg-zinc-100",
+            "text": "text-white dark:text-black",
+            "border": "border-zinc-600/20 dark:border-zinc-400/20",
+        }
 
     def get_css_classes(self) -> dict[str, str]:
         mapping = {
-            "cyan": {"bg": "bg-brand-cyan/10", "text": "text-brand-cyan"},
-            "pink": {"bg": "bg-brand-pink/10", "text": "text-brand-pink"},
+            "cyan": {
+                "bg": "bg-brand-cyan/10",
+                "text": "text-brand-cyan",
+                "border": "border-brand-cyan/20",
+            },
+            "pink": {
+                "bg": "bg-brand-pink/10",
+                "text": "text-brand-pink",
+                "border": "border-brand-pink/20",
+            },
             "neutral": self.get_fallback_css(),
         }
         return mapping.get(self.colour, self.get_fallback_css())