fix: more robust tags parsing

quartz/plugins/transformers/frontmatter.ts

@@ -49,13 +49,21 @@ export const FrontMatter: QuartzTransformerPlugin<Partial<Options> | undefined>
               data.title = file.stem ?? "Untitled"
             }
 
-            if (data.tags && !Array.isArray(data.tags)) {
+            if (data.tags) {
+              // coerce to array
+              if (!Array.isArray(data.tags)) {
                 data.tags = data.tags
                   .toString()
                   .split(oneLineTagDelim)
                   .map((tag: string) => tag.trim())
               }
 
+              // remove all non-string tags
+              data.tags = data.tags
+                .filter((tag: unknown) => typeof tag === "string" || typeof tag === "number")
+                .map((tag: string | number) => tag.toString())
+            }
+
             // slug them all!!
             data.tags = [...new Set(data.tags?.map((tag: string) => slugTag(tag)))]