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/templates/QC.md

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+# @TITLE@
+
+## Metadata
+| Key | Value |
+| --- | --- |
+| ID | @ID@ |
+| CrossReference | @CROSSREF@ |
+
+## Version History
+| Date | Status | Author | Reviewer | Change | Commit |
+| --- | --- | --- | --- | --- | --- |
+| @DATE@ | Accepted | @AUTHOR@ | <reviewer S-ID> | Initial version | pending |
+
+Allowed Status values: `Proposed`, `Accepted`, `Rejected`, `Deprecated`. The latest reviewed row is `Accepted`; the row before it is `Deprecated`.
+
+---
+
+## Purpose
+
+<Why this artifact type matters and what decision it supports.>
+
+## Quality Criteria Checklist
+
+Level: **Mandatory** criteria are the baseline every instance must meet; **Optional** criteria are advanced and may be deferred.
+
+| # | Criterion | Level | ISO/IEC 25010 Characteristic(s) | Notes |
+| --- | --- | --- | --- | --- |
+| 1 | <criterion> | Mandatory | <characteristic(s)> | |
+
+## Common Defects
+
+- <anti-pattern 1>
+- <anti-pattern 2>
+
+## Traceability Rule
+
+- Backward: <what this artifact must link to as input> ([QC-<BACKWARD-SHORT-NAME>-<NNN>])
+- Forward: <what this artifact must feed into as output> ([QC-<FORWARD-SHORT-NAME>-<NNN>])
+
+---
+
+@LINKS@