BOLT-1103: BOLT-1059 follow-up — fix pollItronVtn + smoke poll review comments

Follow-up on merged PR #11453 (BOLT-1059). Address 4 post-merge bot review comments on polling.ts (Cursor: empty VTN body skips poll; unexpected OK payloads return false success), itron-smoke-poll.ts (Cursor: invalid env crashes — apply parseEnv pattern from BOLT-1088), and itron-smoke-poll-raw.ts (CodeRabbit: parseError must capture non-Error exceptions). Branch: artem-agent/bolt-1059-followup-review-fixes. Open PR linked to BOLT-1103. See Linear: https://linear.app/texture/issue/BOLT-1103