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

.agents/skills/artifact/references/ERD.md

@@ -0,0 +1,22 @@
+# Entity Relationship Diagram (ERD) (ERD)
+
+Cite in `CrossReference` only if the instance exists (`new-artifact.sh` checks this for you):
+
+- **DCD** — **Required source**: classes/attributes each entity persists; data types must match
+
+## Required sections (after Metadata / Version History)
+
+1. **Purpose and Scope**.
+2. **Diagram** — PlantUML entity diagram with PK/FK marked on every entity and
+   cardinality (1:1, 1:N) on every relationship; N:M relationships resolved
+   through explicit junction entities.
+3. **Entity Table** — per entity: `Attribute | Type | PK/FK | Nullable |
+   Source (DCD class.attribute)`. Types consistent with the DCD; consistent
+   naming, no implementation-specific abbreviations.
+4. **Relationship Table** — `Entity | Cardinality | Entity | FK | Rule`.
+5. **Normalization Notes** — 3NF confirmed; any denormalization documented
+   with its performance justification.
+
+## Terminology
+
+Entity and column names follow the IT terms from the dictionary (`DICT`), not the PO terms the Domain Model uses.