feat(blog): live in-page filter via data-search attributes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/molecules/BlogSearch.astro

@@ -80,3 +80,65 @@
     }
   }
 </style>
+
+<script>
+  // Lives on /blog. No-ops gracefully on any other page (selectors return empty).
+  const input = document.querySelector<HTMLInputElement>(".binput");
+  if (input) {
+    const rows = Array.from(
+      document.querySelectorAll<HTMLElement>("[data-search]")
+    );
+    const featured = document.querySelector<HTMLElement>("[data-featured]");
+    const yearHeads = Array.from(
+      document.querySelectorAll<HTMLElement>("[data-year-head]")
+    );
+    const empty = document.querySelector<HTMLElement>("[data-empty]");
+    const emptyQuery = empty?.querySelector<HTMLElement>("[data-empty-query]");
+
+    function applyFilter() {
+      const raw = input!.value.toLowerCase().trim();
+      const tokens = raw.length ? raw.split(/\s+/) : [];
+      const isFiltering = tokens.length > 0;
+
+      let visibleCount = 0;
+      for (const row of rows) {
+        const haystack = row.dataset.search ?? "";
+        const isFeatured = row === featured;
+        let visible: boolean;
+        if (!isFiltering) {
+          visible = true;
+        } else if (isFeatured) {
+          // Featured hides whenever there's a query, regardless of match.
+          visible = false;
+        } else {
+          visible = tokens.every((t) => haystack.includes(t));
+        }
+        row.classList.toggle("is-hidden", !visible);
+        if (visible && !isFeatured) visibleCount += 1;
+      }
+
+      // Hide year heads whose following rows are all hidden.
+      for (const head of yearHeads) {
+        let anyVisible = false;
+        let node: Element | null = head.nextElementSibling;
+        while (node && !node.matches("[data-year-head]")) {
+          if (node.matches("[data-search]") && !node.classList.contains("is-hidden")) {
+            anyVisible = true;
+            break;
+          }
+          node = node.nextElementSibling;
+        }
+        head.classList.toggle("is-hidden", !anyVisible);
+      }
+
+      // Toggle empty-state message.
+      if (empty) {
+        const showEmpty = isFiltering && visibleCount === 0;
+        empty.hidden = !showEmpty;
+        if (showEmpty && emptyQuery) emptyQuery.textContent = input!.value.trim();
+      }
+    }
+
+    input.addEventListener("input", applyFilter);
+  }
+</script>