Fix epoch filter strict equality mismatch with numeric frontmatter values

fmParseScalarValue converts numeric-looking YAML values to JS numbers,
but filter_epoch from the zod schema is always a string. Wrap the
frontmatter epoch in String() so strict equality works regardless of
the parsed type.

Author: cursoragent

workers/src/orchestrate.ts

@@ -665,7 +665,7 @@ async function runCatalog(
     // Server-side epoch filter — deterministic, cheap, correct
     if (filter_epoch) {
       candidates = candidates.filter(
-        (e) => e.frontmatter && (e.frontmatter as Record<string, unknown>).epoch === filter_epoch,
+        (e) => e.frontmatter && String((e.frontmatter as Record<string, unknown>).epoch) === filter_epoch,
       );
     }