fix(portals): make facet chips keyboard-operable and reject zero years

- The chips were plain spans with a click handler, so the whole feature
  was mouse-only. Actionable chips are <button> now (focusable, Enter and
  Space activate); a year chip that cannot be discovered by stays an
  informational span rather than becoming a disabled button. The button
  chrome is neutralized so they render identically to the chips beside
  them, with a visible focus ring.

- `0000-00-00`, the placeholder providers ship for "no date", read as a
  four-digit year: the chip offered it, and the request then dropped the
  filter because 0 is falsy, so the page answered with unfiltered popular
  titles. `isTmdbYearFacet()` now gates both the chip and the route
  params, so a deep link cannot reach a state the chips refuse to offer.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

libs/ui/components/src/lib/content-hero/content-hero.component.scss

@@ -320,8 +320,15 @@
             border-color: rgba(255, 215, 0, 0.3);
         }
 
+        // Rendered as a <button> so the facet is keyboard-operable; the
+        // UA's own font and appearance have to be neutralized to keep it
+        // visually identical to the informational chips beside it.
         &--clickable {
+            appearance: none;
             cursor: pointer;
+            font-family: inherit;
+            letter-spacing: inherit;
+            line-height: inherit;
             transition:
                 border-color 0.15s ease,
                 background 0.15s ease;
@@ -330,6 +337,11 @@
                 background: var(--tag-border);
                 border-color: var(--text-secondary, rgba(255, 255, 255, 0.5));
             }
+
+            &:focus-visible {
+                outline: 2px solid var(--text-primary, #fff);
+                outline-offset: 2px;
+            }
         }
     }
 

libs/ui/components/src/lib/portal-detail-shell/content-about.component.scss

@@ -83,8 +83,15 @@
         border-color: rgba(255, 215, 0, 0.3);
     }
 
+    // Rendered as a <button> so the facet is keyboard-operable; the UA's
+    // own font and appearance have to be neutralized to keep it visually
+    // identical to the informational chips beside it.
     &--clickable {
+        appearance: none;
         cursor: pointer;
+        font-family: inherit;
+        letter-spacing: inherit;
+        line-height: inherit;
         transition:
             border-color 0.15s ease,
             background 0.15s ease;
@@ -93,6 +100,11 @@
             background: var(--tag-border, rgba(255, 255, 255, 0.2));
             border-color: var(--text-secondary, rgba(255, 255, 255, 0.5));
         }
+
+        &:focus-visible {
+            outline: 2px solid var(--text-primary, #fff);
+            outline-offset: 2px;
+        }
     }
 }