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/VpxTransform.md

@@ -0,0 +1,43 @@
+# VpxTransform
+
+`class VpxTransform` — inherits [Transform](../classes/Transform.md)
+
+Defined in [transform_vpx.hpp:23](../../../../src/system/transform_vpx.hpp#L23)
+
+## Public Types
+
+### `using VpxTransform::ColTable = std::map<char, char>`
+
+📍 [transform_vpx.hpp:26](../../../../src/system/transform_vpx.hpp#L26)
+
+## Private Attributes
+
+### `std::string bkp_kind_`
+
+📍 [transform_vpx.hpp:36](../../../../src/system/transform_vpx.hpp#L36)
+
+### `std::string payload_kind_`
+
+📍 [transform_vpx.hpp:37](../../../../src/system/transform_vpx.hpp#L37)
+
+### `std::vector< ColTable > bkp_to_payload_`
+
+📍 [transform_vpx.hpp:38](../../../../src/system/transform_vpx.hpp#L38)
+
+### `std::vector< ColTable > payload_to_bkp_`
+
+📍 [transform_vpx.hpp:39](../../../../src/system/transform_vpx.hpp#L39)
+
+## Public Functions
+
+### `VpxTransform(std::string name, std::string bkp_kind, std::string payload_kind, std::vector< ColTable > bkp_to_payload, std::vector< ColTable > payload_to_bkp)`
+
+📍 [transform_vpx.hpp:28](../../../../src/system/transform_vpx.hpp#L28)
+
+### `std::vector< std::pair< Pin *, Pin * > > apply(Part *a, Part *b) const override`
+
+📍 [transform_vpx.hpp:33](../../../../src/system/transform_vpx.hpp#L33)
+
+---
+
+← [Back to classes](index.md) · [Top](../index.md)