Dimensional yml/doc alignment pass (OpenMetadata-verified drift) #2386

Description/Context

Batch of OpenMetadata-verified doc-vs-SQL mismatches in models/dimensional:

1. afact_video_engagement.video_played_count / video_completed_count documented as 0/1 flags but are counts; afact_discussion_engagement "indicating if" columns are count_if.
2. tfact_video_events yml lists event types not in the SQL filter (video_hide_transcript) and omits ones that are (complete_video, closed_captions); tfact_course_navigation_events yml lists edx.ui.lms.video.played which isn't filtered.
3. dim_discussion_topic.discussion_type yml values don't match emitted 'discussion component' / 'course-wide discussion'.
4. tfact_payment yml describes user_fk resolution via an order chain but the SQL joins staging orders directly (lines 46-58); also switch its watermark from > to >= (line 145; siblings use >=) and add the standard dedup guard.
5. dim_video extracts $.edx_video_id twice as edx_video_id and video_edx_uuid, documented as different identifiers.
6. OpenMetadata-confirmed type drift: dim_user.certificate_desired is VARCHAR but documented boolean; mitlearn_openedx_user_id / mitxonline_application_user_id are BIGINT but documented string.

Plan/Design

Reconcile each yml/doc entry to the actual SQL behavior (or fix the SQL where the doc reflects intent, e.g. the tfact_payment watermark). Mechanical documentation-alignment pass; verify each against OpenMetadata profiling.

P2. Part of #2375 (2026-07 dbt warehouse audit). Witan task: tk-dimensional-yml-doc-alignment-pass-openmetadata--1f9c93.