Auto-generated API doc: doxygen → custom Python emitter → doc/api/.

`cmake --build build --target doc` runs Doxygen to produce XML, then
`doc/gen_api_md.py` (~330 lines, stdlib-only) emits a Markdown tree
under `doc/api/` that gitea renders directly in its file browser.

- 24 class/struct pages + 51 source-file pages + indices, with source
  links of the form `../../../../src/...#L42` that gitea turns into
  clickable line-anchored links.
- Doxyfile.in templated by CMake (XML-only output to build/doc/xml/).
- Pure Python emitter, zero external deps — no doxybook2 (not packaged
  on Arch) and no moxygen (avoids Node).
- Target gracefully disabled if Doxygen or Python 3 is missing at
  configure time; regular build target unaffected.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

doc/api/classes/Part.md

@@ -0,0 +1,45 @@
+# Part
+
+`class Part` — inherits [SystemElementContainer< Pin >](../classes/SystemElementContainer.md)
+
+Defined in [parts.hpp:11](../../../../src/system/parts.hpp#L11)
+
+Forward declaration of the [Module](../classes/Module.md) class. class.
+
+## Public Attributes
+
+### `Module * prnt`
+
+📍 [parts.hpp:16](../../../../src/system/parts.hpp#L16)
+
+Pointer to the parent module.
+
+### `std::string connector_type`
+
+📍 [parts.hpp:17](../../../../src/system/parts.hpp#L17)
+
+Tag used by the transform registry; empty = untyped.
+
+### `ComponentKind kind`
+
+📍 [parts.hpp:18](../../../../src/system/parts.hpp#L18)
+
+Inferred from the part name's reference-designator prefix.
+
+## Public Functions
+
+### `Part(std::string name)`
+
+📍 [parts.hpp:14](../../../../src/system/parts.hpp#L14)
+
+### `~Part()`
+
+📍 [parts.hpp:15](../../../../src/system/parts.hpp#L15)
+
+### `void add(Pin *pin) override`
+
+📍 [parts.hpp:19](../../../../src/system/parts.hpp#L19)
+
+---
+
+← [Back to classes](index.md) · [Top](../index.md)