Split vulkan_window.cpp by responsibility and render() into phases

VulkanWindow's 3000-line TU becomes sdl_window.cpp (window, events,
cursor, screenshot BMP), vk_device.cpp (device, swapchain, MSAA,
framebuffers), vk_pipelines.cpp (render passes, pipelines),
vk_resources.cpp (buffers, render targets, geometry), vk_textures.cpp
(textures, samplers, descriptors), vk_frame.cpp (render) and
ui_batches.cpp; vulkan_window.cpp keeps construction and timing stats.
Function bodies move verbatim.

render() now reads fence/acquire -> prepare_draws -> prepare_ui ->
write_draw_states -> record_passes -> record_readbacks -> submit ->
finish_readbacks -> present, with FrameDraws / Readback carrying the
locals that used to live across 500 lines.

Verified: login-screen screenshot byte-identical to HEAD; game-world
draw/vertex/index/UI counts identical; ctest, port_gate macos+android,
Android build pass.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.agents/skills/metin2-40250-parity-audit/references/project-map.md

@@ -33,7 +33,7 @@
 - `src/port/<Lib>/<File>.{h,cpp}` — mirror of each 40250 `logic`/`python` unit (see SKILL.md "Code layout").
 - `src/platform/` — implementations of the mirrored 40250 platform classes (D3D8 recorder, Granny,
   Miles, SpeedTree stand-in, window/input, ScriptLib boot).
-- `src/host/` — SDL3 + Vulkan host (`main.cpp` entry, `live_client.cpp` loop, `vulkan_window.cpp` renderer); `src/gr2/` — Granny reader; `src/codepage/` — code pages.
+- `src/host/` — SDL3 + Vulkan host (`main.cpp` entry, `live_client.cpp` loop, `vulkan_window.h` renderer split across `vulkan_window.cpp`/`vk_*.cpp`/`sdl_window.cpp`/`ui_batches.cpp`); `src/gr2/` — Granny reader; `src/codepage/` — code pages.
 - `third_party/` — vendored cpython 2.7.18, cryptopp, freetype, minilzo.
 - `tests/port/` — port tests and the fake login server; `tests/gr2/` — Granny reader tests.
 - `android/` — SDLActivity shell, `android/build.sh`, `android/push-client.sh`.