refactor: simplify spark button injection logic

Update the spark button injection to use `data-spark` slugs on
`md-table` elements instead of manual table parsing. This improves
reliability by leveraging the slug generated during markdown
rendering.

src/components/stores/reveal.ts

@@ -183,8 +183,6 @@ const LINK_SVG =
 
 // ---- Spark button (tables) ----
 
-const DICE_HEADER_RE = /^d\d+$/i;
-
 function injectSparkButtons(
   root: Element,
   normalizedPath: string,
@@ -196,40 +194,24 @@ function injectSparkButtons(
   );
   if (pageTables.length === 0) return;
 
-  const tables = root.querySelectorAll("table");
-  tables.forEach((table) => {
-    // Find the first header row — check thead first, then first tr
-    const thead = table.querySelector("thead");
-    const firstRow =
-      thead?.rows[0] ??
-      table.querySelector("tbody tr:first-child, tr:first-child");
-    if (!firstRow || !(firstRow instanceof HTMLTableRowElement)) return;
+  // Spark tables are rendered as <md-table data-spark="columnSlug">
+  const sparkTables = root.querySelectorAll("md-table[data-spark]");
+  sparkTables.forEach((el) => {
+    const colSlug = el.getAttribute("data-spark");
+    if (!colSlug) return;
 
-    const firstCell = firstRow.cells[0];
-    if (!firstCell) return;
-    const firstHeader = firstCell.textContent?.trim() ?? "";
-    if (!DICE_HEADER_RE.test(firstHeader)) return;
-
-    // Collect data headers from the remaining cells
-    const dataHeaders: string[] = [];
-    for (let i = 1; i < firstRow.cells.length; i++) {
-      const text = firstRow.cells[i].textContent?.trim() ?? "";
-      if (text) dataHeaders.push(text);
-    }
-
-    // Match against completions: find the spark table with matching
-    // notation and data headers (order matters)
-    const match = pageTables.find(
-      (st) =>
-        st.notation.toLowerCase() === firstHeader.toLowerCase() &&
-        st.headers.length === dataHeaders.length &&
-        st.headers.every((h, i) => h === dataHeaders[i]),
-    );
+    // Find the matching completions entry by column slug
+    const match = pageTables.find((st) => {
+      // st.slug is the combined slug (pageName-columnSlug);
+      // colSlug is just the column part. Match by checking if
+      // the combined slug ends with the column slug.
+      return st.slug.endsWith(`-${colSlug}`);
+    });
     if (!match) return;
 
-    // Inject the spark button
+    // Inject the spark button into the <md-table> wrapper
     const btn = createSparkButton(match.slug);
-    const wrapper = table.parentElement;
+    const wrapper = el.parentElement;
     if (wrapper) {
       wrapper.style.position = "relative";
       wrapper.classList.add("group");