Add planning baseline: BC, SA, PP and two gateways

Create the Business Case, Stakeholder Analysis (S01 course participant,
S02 Udemy coursists, S03 GitHub viewers), Project Plan and the milestone
documents MIL-001 (project setup, 6 tasks) and MIL-002 (game
implementation, 8 tasks) for the console Blackjack game.

Register PP and MIL in the artifact registry, set the PO language to en,
and link the synced Gitea milestones in the Gateway Schedule.

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.agents/skills/artifact/references/TRR.md

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+# Reviewer Training Record (TRR)
+
+The project's record that a reviewer training session happened: the evidence
+that mitigates the "resistance to standardized reviews" risk and satisfies a
+"training delivered and recorded" gateway criterion. It records one session
+of the framework's training material (`TRN`); it holds project data
+(stakeholder IDs, dates), so it lives in the project, not in the framework.
+
+- **File:** `docs/sqa/reviewer-training-record.md` (one per project; add a new
+  row under `## Attendees and Assessment` and a Version History row for each
+  further session).
+- **Create:** `new-artifact.sh TRR --file docs/sqa/reviewer-training-record.md
+  --cite TRN-001=framework/process/reviewer-training.md`.
+- **CrossReference:** `TRN` (the material that was taught).
+
+## Required sections (after Metadata / Version History)
+
+Session (material, date, facilitator, format), Attendees and Assessment
+(stakeholder IDs, attended, Pass or Not yet against the assessment in the
+material), Feedback, Follow-ups (action, owner as a stakeholder ID, due).
+Fill the record after the session; never before.