Add Pretty Table project: plan, accepted documents and code

Business Case, Stakeholder Analysis, Project Plan and milestone MIL-001
with review records RC-001 to RC-003, then the Python project: PrettyTable
Pokemon table, constants, pytest tests, pyproject.toml, Doxyfile, CI
workflow and README.

Task: MIL-001#1
Task: MIL-001#2
Task: MIL-001#3
Task: MIL-001#4
Task: MIL-001#5
Task: MIL-001#6
Task: MIL-001#7
Task: MIL-001#8

.claude/skills/artifact/references/TM.md

@@ -0,0 +1,18 @@
+# Traceability Matrix (TM)
+
+One matrix per project: `docs/sqa/traceability-matrix.md`. It makes the
+Business Case's cross-artifact traceability target measurable.
+
+## Required sections (after Metadata / Version History)
+
+- **Purpose**.
+- **Traceability Table** — one row per artifact instance:
+  `Artifact Instance | Type | Language | Domain | Upstream (Backward Link) |
+  Downstream (Forward Link) | Last Reviewed (RC-ID)`. `Language` and `Domain`
+  copy the artifact's Metadata rows so a reviewer can pick the right reviewer
+  from the matrix; they are `-` for a technical type (OC, SD, DCD, ERD, ADR,
+  TM, RC, QC, source code). `check-languages.sh --list` prints the same values.
+  Add or update a row whenever an instance is created or reviewed.
+- **Coverage Notes** — which types have no instance yet, and how to read
+  `-`: in Upstream it means foundational; in Downstream it means nothing
+  is built on it yet; in Last Reviewed it means no `RC-*` exists yet.