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/app.tsx

@@ -35,10 +35,8 @@ function AppLayout(props: { children: any }) {
   let lastScrollY = 0;
 
   onMount(() => {
-    // Initialize performance tracking
     initPerformanceTracking();
 
-    // Start monitoring for new deployments
     startDeploymentMonitoring();
 
     const windowWidth = createWindowWidth();