Wire test labeler pipeline into CLI and exit codes
Updates LabelerCmd::run to parse target, build HTTP/DNS clients,
run the pipeline, render the report with color control, and return
appropriate exit codes. Propagates ExitCode through the dispatch chain
(TestCmd -> Command -> cli::run -> main).
Threading no_color flag through from root Cli through dispatch.
ReportHeader is populated from IdentityFacts when available.
Verifies test-labeler.AC6.1 (partial) and AC6.6 (NO_COLOR honored).
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>