chore(node-sdk): audit src core

Align response types with the Backend (webhooks, me, health, operation payload, error codes, admin actions), shorten comments, drop section banners.

Claude-Session: https://claude.ai/code/session_01Agoc9bRVE9KL7mmWtey9Vq

src/utils.ts

@@ -1,17 +1,10 @@
 import crypto from 'node:crypto';
 
-/**
- * Generate a UUIDv7 (time-ordered UUID per RFC 9562).
- *
- * Layout (128 bits):
- *   48-bit Unix timestamp (ms) | 4-bit version (7) | 12-bit rand_a
- *   2-bit variant (10) | 62-bit rand_b
- */
+// UUIDv7 (RFC 9562): 48-bit ms timestamp, version 7, variant 10, 74 random bits
 export function uuidv7(): string {
   const now = Date.now();
   const random = crypto.randomBytes(10);
 
-  // Bytes 0-5: 48-bit timestamp (ms)
   const bytes = Buffer.alloc(16);
   bytes[0] = (now / 2 ** 40) & 0xff;
   bytes[1] = (now / 2 ** 32) & 0xff;
@@ -20,11 +13,9 @@ export function uuidv7(): string {
   bytes[4] = (now / 2 ** 8) & 0xff;
   bytes[5] = now & 0xff;
 
-  // Bytes 6-7: version (0111) + 12 bits random
   bytes[6] = 0x70 | (random[0]! & 0x0f);
   bytes[7] = random[1]!;
 
-  // Bytes 8-15: variant (10) + 62 bits random
   bytes[8] = 0x80 | (random[2]! & 0x3f);
   bytes[9] = random[3]!;
   bytes[10] = random[4]!;
@@ -44,25 +35,16 @@ export function uuidv7(): string {
   );
 }
 
-/**
- * Generate a random nonce: 16 random bytes, base64url encoded.
- */
 export function generateNonce(): string {
   const bytes = crypto.randomBytes(16);
   return base64urlEncode(bytes);
 }
 
-/**
- * Encode a Buffer or Uint8Array to base64url (no padding, RFC 4648 section 5).
- */
 export function base64urlEncode(data: Buffer | Uint8Array): string {
   const buf = Buffer.isBuffer(data) ? data : Buffer.from(data);
   return buf.toString('base64url');
 }
 
-/**
- * Decode a base64url string (no padding) to a Buffer.
- */
 export function base64urlDecode(input: string): Buffer {
   return Buffer.from(input, 'base64url');
 }