Add injection-level tracking domain error codes (2009-2012)

[rosadajake]

Document the new Transmission-family extended error codes returned by POST /api/v1/transmissions when a supplied tracking_domain fails validation: 2009 (unconfigured), 2010 (unverified), 2011 (compliance pending), and 2012 (blocked). All return HTTP 400.

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Note

Low Risk
Documentation-only change to the extended error codes table; no runtime or API behavior changes in this PR.

Overview
Updates the Extended Error Codes doc with four new Transmission codes (2009–2012) for failures when a tracking_domain on injection/transmissions is invalid. Each maps to HTTP 400 and includes corrective-action guidance (configure domain, verify via CNAME/POST /api/v1/tracking-domains/{domain}/verify, wait on compliance, or switch domain / contact Support).

Also refreshes the page lastUpdated metadata.

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