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/DICT.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 |
+
+---
+
+## Purpose and Scope
+
+Maps each Product Owner (PO) term to its professional IT term. PO language:
+<language, from the registry's `Languages` section>.
+
+## Dictionary
+
+| PO term | Language | IT term | Definition | Used as PO term in | Used as IT term in |
+| --- | --- | --- | --- | --- | --- |
+| <term> | <da> | <Term> | <one sentence, in the PO language> | DM | OC, SD, DCD, ERD |
+
+## Rules
+
+- The Domain Model, use cases and user stories use the PO term; the Operation
+  Contract, Sequence Diagram, Design Class Diagram and ERD use the IT term.
+- One IT term per PO term and one PO term per IT term; no synonyms.
+
+---
+
+@LINKS@