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/server/nessa-auth.test.ts

@@ -57,7 +57,6 @@ describe("verifyNessaToken with Clerk JWT", () => {
     expect(result.exp).toBe(mockPayload.exp);
     expect(result.iat).toBe(mockPayload.iat);
 
-    // Verify verifyToken was called with correct options
     expect(mockVerifyToken).toHaveBeenCalledWith(
       "valid-clerk-session-token",
       expect.objectContaining({