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/Modules.md

@@ -0,0 +1,27 @@
+# Modules
+
+`class Modules` — inherits [SystemElementContainer< Module >](../classes/SystemElementContainer.md)
+
+Defined in [modules.hpp:23](../../../../src/system/modules.hpp#L23)
+
+## Public Functions
+
+### `Modules(void)`
+
+📍 [modules.hpp:26](../../../../src/system/modules.hpp#L26)
+
+### `Modules(std::vector< Module * > parts)`
+
+📍 [modules.hpp:27](../../../../src/system/modules.hpp#L27)
+
+### `void add(Module *module)`
+
+📍 [modules.hpp:28](../../../../src/system/modules.hpp#L28)
+
+### `~Modules()`
+
+📍 [modules.hpp:29](../../../../src/system/modules.hpp#L29)
+
+---
+
+← [Back to classes](index.md) · [Top](../index.md)