Instrument 'Pipeline results reviewed' funnel metric for AI Pipeline Builder

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Track when a user first views the pipeline results page for a project whose CI config was AI-generated. This is the Pipeline results reviewed funnel metric from the north-star metrics issue.

Scope (initial): pipeline details page (/-/pipelines/278964) only, fired once per project, gated to pipelines created at or after the AI config commit.

Implementation: !241602 (merged)

Open question: The CI Expert agent currently links users to the MR (not the pipeline details page). Should the MR pipeline widget also count as a result-review surface? Pending input from @manuelgrabowski and @csaez-ext on this note.