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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.claude/skills/artifact/references/BC.md

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+# Business Case (BC)
+
+Cite in `CrossReference` only if the instance exists (`new-artifact.sh` checks this for you):
+
+- **SA** — Stakeholders section — cite S-IDs instead of re-describing roles
+- **BMC** — Cost–Benefit Assessment must agree with its cost/revenue blocks
+- **BPMN** — Forward: the process that realizes the objectives
+- **KPI** — Success Criteria — each criterion is operationalized by a KPI
+- **UCD** — Forward: scope expressed as actors and goals
+
+## Required sections (after Metadata / Version History)
+
+In this order:
+
+1. **Executive Summary** — one paragraph framing the problem and the
+   proposed solution.
+2. **Methodological and Standards Foundation** — states the methodology
+   (e.g. Larman's *Applying UML and Patterns*) and quality standards (e.g.
+   ISO/IEC 25002/25010/25019) the rest of the document and downstream
+   artifacts are built on.
+3. **Problem Statement** — the recurring problems that justify the project.
+4. **Business Opportunity** — what becomes possible if the problem is
+   solved.
+5. **Objectives** — concrete, verifiable statements of what the project
+   will achieve.
+6. **Scope** — split into `## In Scope` and `## Out of Scope` subsections.
+7. **Expected Benefits** — split into `### Tangible Benefits` and
+   `### Intangible Benefits`.
+8. **Strategic Alignment** — how the project supports organizational goals.
+9. **Success Criteria** — a table with explicit, measurable targets (not
+   aspirations).
+10. **Risks** — a table with `Risk | Impact | Mitigation` columns; every
+    risk must have a mitigation.
+11. **Assumptions** — bullet list, kept distinct from Constraints.
+12. **Constraints** — bullet list, kept distinct from Assumptions.
+13. **Cost–Benefit Assessment** — a table (`Costs | Benefits`); may be
+    qualitative if explicitly justified.
+14. **Stakeholders** — a table referencing exact stakeholder IDs from the
+    project's Stakeholder Analysis (e.g. `S01`, `S07`) if `SA` exists per
+    the CrossReference check above. **Never re-describe stakeholder roles
+    inline instead of citing their IDs** — this is the single most common
+    defect found when reviewing Business Cases (see `QC-BC-001`'s Common
+    Defects).
+15. **Recommendation** — a single, unambiguous "proceed" or "do not
+    proceed" statement.