docs: centralize Markdown developer manual

docs/book.toml

@@ -0,0 +1,21 @@
+[book]
+title = "Kaptan Developer Manual"
+description = "Architecture, board bring-up, simulation, and contributor guidance for Kaptan."
+authors = ["Kaptan contributors"]
+language = "en"
+src = "src"
+
+[build]
+# Keep generated site files out of the Markdown source tree.
+build-dir = "../target/docs"
+create-missing = false
+
+[output.html]
+default-theme = "light"
+preferred-dark-theme = "navy"
+git-repository-url = "https://github.com/Orkavian/kaptan"
+edit-url-template = "https://github.com/Orkavian/kaptan/edit/main/{path}"
+additional-css = ["theme/kaptan.css"]
+additional-js = ["theme/kaptan.js"]
+fold = { enable = true, level = 1 }
+smart-punctuation = true