build: Ninja Multi-Config, schema codegen, and the offline-mod FPS cap endpoint

[Seltraeh]

build: Ninja Multi-Config, schema codegen, and the offline-mod FPS cap endpoint

Branch: split/01-build-structural
Base: dev

Build-system and plumbing changes only. No gameplay behaviour is touched.

What's included

• CMakePresets.json — replaces the Visual Studio 17 2022 generator with Ninja Multi-Config, so the build no longer pins a platform toolset and works on 2022 and 2026+ alike. Adds paired Debug/Release build presets.
• CMakeLists.txt — wires the packet-generator into the build. gimuserver/packets/all.hpp and gimuserver/archive/archive.hpp are regenerated whenever a .kdl changes, replacing the hand-run generate.py.
• OfflineModController (new) — one route, GET /offline_mod/fps_cap, returning the configured render cap as a bare integer. Consumed by the offline-proxy render hook at startup, not by the game client; the proxy falls back to its compile-time default if unreachable.
• standalone_frontend — optional config path as argv[1] with a chdir to its parent, so relative paths in config.json resolve regardless of launch directory. stdout unbuffered so headless/redirected boot logs survive a crash.
• bootstrap_windows.cpp — MSVC wants __declspec(dllexport) before the return type. The __APPX__ block had never been compiled (debug-win64 builds STANDALONE), so this C2059 only appeared on the first release build.
• vcpkg.json — drops drogon[ctl]. The port marks it supports:"native" and vcpkg refuses it on x86-windows-static. drogon_ctl is a scaffolding CLI this codebase never calls.
• packet-generator — submodule bumped to 1e1682e.
• BadgeInfo.cpp — serialises ::BadgeInfoResp rather than ::BadgeInfo, so the response carries the h23iRjGN dispatch key at its root. Needs the wrapper struct from the submodule bump, which is why it rides along here.
• Dispatcher — handler exceptions are now written to the request log alongside the existing LOG_ERROR.

Review focus

The submodule bump is the only real risk. It carries gatcha→gacha renames, a user_level_mst field rename to energy, and unit KDL type corrections. Those were validated inside the combined branch — this is the first time they are compiled against dev alone.

Verification

Clean configure and build, Debug and Release. GET /offline_mod/fps_cap returns 200 with the configured value.