feat(telemetry): respect DO_NOT_TRACK environment variable

[CtriXin]

Summary

DO_NOT_TRACK=1 or DO_NOT_TRACK=true now opts out of telemetry, matching the standard env var convention.

Change: added check in maybe_ping() after the existing RTK_TELEMETRY_DISABLED check.

Fixes: #1514

Test Plan

• cargo test telemetry — 16 tests pass
• Manual: DO_NOT_TRACK=1 rtk gain produces no telemetry ping

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[pszymkowiak]

[w] wshm · Automated triage by AI

📊 Automated PR Analysis

✨ Type	feature
🟢 Risk	low

Summary

Adds support for the standard DO_NOT_TRACK environment variable to opt out of telemetry. When DO_NOT_TRACK is set to "1" or "true" (case-insensitive), telemetry pings are suppressed, checked right after the existing RTK_TELEMETRY_DISABLED guard.

Review Checklist

• Tests present
• Breaking change
• Docs updated

Linked issues: #1514

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Analyzed automatically by wshm · This is an automated analysis, not a human review.