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/components/icons/BackArrow.tsx

@@ -1,29 +0,0 @@
-const BackArrow = (props: {
-  height: number;
-  width: number;
-  stroke: string;
-  strokeWidth: number;
-  class?: string;
-}) => {
-  return (
-    <div class={props.class}>
-      <svg
-        xmlns="http://www.w3.org/2000/svg"
-        fill="none"
-        viewBox="0 0 24 24"
-        strokeWidth={props.strokeWidth}
-        stroke={props.stroke}
-        height={props.height}
-        width={props.width}
-      >
-        <path
-          strokeLinecap="round"
-          strokeLinejoin="round"
-          d="M10.5 19.5L3 12m0 0l7.5-7.5M3 12h18"
-        />
-      </svg>
-    </div>
-  );
-};
-
-export default BackArrow;

src/components/icons/MenuBars.tsx

@@ -1,39 +0,0 @@
-function MenuBars() {
-  return (
-    <svg
-      width="36"
-      height="30"
-      viewBox="0 0 120 100"
-      fill="none"
-      xmlns="http://www.w3.org/2000/svg"
-    >
-      <g id="Mask group">
-        <g id="Frame 1">
-          <rect width="120" height="100" />
-          <line
-            id="LineA"
-            x1="11.5"
-            y1="31.5"
-            x2="108.5"
-            y2="31.5"
-            strokeWidth="6"
-            strokeLinecap="round"
-            class="stroke-black dark:stroke-white"
-          />
-          <line
-            id="LineB"
-            x1="11.5"
-            y1="64.5"
-            x2="108.5"
-            y2="64.5"
-            strokeWidth="6"
-            strokeLinecap="round"
-            class="stroke-black dark:stroke-white"
-          />
-        </g>
-      </g>
-    </svg>
-  );
-}
-
-export default MenuBars;