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/auth-query.ts

@@ -80,7 +80,6 @@ export const getUserState = query(async (): Promise<UserState> => {
  * Call this after login, logout, token refresh, email verification
  */
 export function revalidateAuth() {
-  // Revalidate the cache
   revalidateKey("user-auth-state");
 
   // Dispatch event to trigger UI updates (client-side only)