chore: remediate pygienium audit findings

Dead code: 77 verified-unused exports, files (BackArrow, MenuBars,
cookies.ts, db/create.ts, schemas/comment.ts, security-headers.ts) and
12 unused dependencies removed
Comments: ~370 RESTATE comments stripped across 53 files; 2 verbose
blocks tightened; dead commented-out config removed
Complexity: bulkUpsert extracted into 11 per-entity helpers (CCN 156->~10);
login formHandler split into 3 submitters (CCN 63->~5); account page render
split into 8 section components (CCN 40); updatePost SQL builder rebuilt;
assert*Owned consolidated behind generic assertOwnedBy
Defensive guards: 4 redundant rethrow/nullish guards removed

src/lib/s3upload.ts

@@ -61,7 +61,6 @@ export default async function AddImageToS3(
       throw new Error("Failed to upload file to S3");
     }
 
-    // Create thumbnails for images (blog posts only)
     if (type === "blog" && isImage) {
       try {
         const thumbnail = await resizeImage(file, 200, 200, 0.8);