Add planning baseline: BC, SA, PP and MIL-001 to MIL-003

Draft and accept the Business Case, Stakeholder Analysis (S01-S03) and
Project Plan for the Day 15 coffee machine assignment. Add three
milestones with 17 tasks, synced to the git host as Milestones 40-42
and Issues #1-#17. Register PP and MIL in the artifact registry and set
the PO language to en.

No issue closed: planning only, no code changed.

docs/artifact-registry.md

@@ -0,0 +1,43 @@
+# Artifact Registry
+
+This project's artifact state. Types, short names and `CrossReference
+Candidates` come from the framework catalog
+(`framework/registry/artifact-catalog.md`); this file only records where
+each document lives in *this* project and the next version to use.
+
+Delete rows for types you don't use. Add a row the first time you create a
+document of a type. `Primary File` may contain a glob (e.g.
+`docs/uc-*/uc.md`); `framework/scripts/find-crossreferences.sh` reads it.
+
+| Short Name | Artifact Type | Primary File | Next Available Version |
+| --- | --- | --- | --- |
+| BC | Business Case | docs/business-case.md | 002 |
+| SA | Stakeholder Analysis | docs/stakeholder-analysis.md | 002 |
+| PP | Project Plan | docs/project-plan.md | 002 |
+| MIL | Milestone / Gateway | docs/milestones/*.md | 004 |
+
+## Languages
+
+Set the PO language when the project starts; `project-planning` asks for it
+if it is missing. A translated artifact is named `<artifact>.<language>.md`
+(for example `business-case.da.md`); the English file stays the source.
+
+| Setting | Value |
+| --- | --- |
+| PO language | en |
+| High-level register | IT Executive English |
+| Technical register | IT Professional English |
+
+| Artifact types | Register | Also kept as a PO-language file |
+| --- | --- | --- |
+| BC, KPI, PP, MIL | IT Executive English | Yes |
+| SA, BMC, BPMN, UCD, US, UC, SSD, DM, RA, GOV, DICT | IT Professional English | Yes |
+| OC, SD, DCD, ERD, ADR, TM, RC, QC, source code | IT Professional English | No |
+
+## Notes
+
+- "Next Available Version" is the zero-padded (3-digit) version to use the
+  *next* time a new document of that type is created. Increment it only when
+  a brand-new document is created, not when an existing document's
+  `## Version History` gets a row.
+- `ADR` uses 4 digits (`0001`); `RC` is sequential across all artifact types.