feat: add wiki build kind with file-structure-derived navigation

- add build_wiki_nav deriving MkDocs nav from docs/wiki file structure
  (index.md -> Home, numeric prefixes stripped and title-cased, nested
  dirs become groups, natural ordering)
- add --wiki / --wiki-dir to build; wiki-only builds need no --module
- merge wiki nav before generated lib/api nav; wiki Home replaces the
  nav spec Home entry
- add mkdocs.wiki.yml template fragment and nav/cli tests
- dogfood doc-forge's own docs/wiki and regenerate site output

docs/wiki/05_development/01_environment.md

@@ -0,0 +1,20 @@
+# Environment Setup
+
+## Create the environment
+
+```bash
+python -m venv .venv
+.venv\Scripts\activate
+pip install -e .
+```
+
+Requires Python 3.11+.
+
+## Dependencies
+
+Development extras include:
+
+- `pytest`, `pytest-cov` — test suite and coverage
+- `ruff` — lint and format checking
+- `black` — auto-formatting
+- `mypy` — strict typing checks