Framework for Sacred 2 Gold, game log mirror, borderless fullscreen

Ported from sacredK with module-relative addresses, hooks by exported
name and a SHA-256 check of the six game modules (Community Patch
2.65.1). Borderless windowed at monitor size replaces exclusive
fullscreen, whose focus loss during loading made the game quit and
crash on exit.

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

docs/borderless.md

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+# Borderless fullscreen
+
+Request (2026-10-31): make the game start without crashing, then borderless
+fullscreen as the first feature.
+
+## The start-up crash
+
+Measured 2026-10-31 (3440x1440, options `video.fullscreen = 1`):
+
+- Started through the launcher from a background process, Windows doesn't
+  hand the game window the foreground. In exclusive fullscreen Direct3D then
+  minimises it (style gains `WS_MINIMIZE` after ~8 s, during "SETUP AI..." on
+  the loading screen), and the game quits ~20 s later. On the way out
+  `s2logicai.dll`'s static destructors call a pure virtual function (a global
+  allocator object at `0x101BF774` is already destroyed), the game's
+  `s2_purecall()` handler (`sacred2.exe` 0x489ada) breaks into the debugger:
+  exception 0x80000003 in KERNELBASE.
+- Started with focus (or directly, unmodified), it reaches the main menu.
+- `cDX9Base::flip` minimises the window and sets device flag 4 when Present
+  returns `D3DERR_DEVICELOST`.
+
+So the crash was exclusive fullscreen losing the focus; it is gone with
+borderless.
+
+## How the mod works (`src/mods/borderless.cpp`)
+
+`cDX9Base::_initDX(const sInitParams&)` (s2render 0x1029a736, exported, the
+only device set-up, reached through `initDX` / `cDX9Advance::initAdvance`)
+has a windowed path: style `0x12c00000`, size clamped to
+`GetSystemMetrics(SM_CXSCREEN/SM_CYSCREEN)` minus the frame, window centred,
+back buffer of that size, presentation interval default. See
+`src/game/render/dx9base.h` for `sInitParams` and the addresses.
+
+- The hook passes `fullscreen = 0` and the primary monitor's size.
+- At startup the four uses of the style constant (0x1029ab49, ab56, ab5b,
+  ab62) become `WS_POPUP | WS_VISIBLE`, so the game's own code makes a
+  frameless window covering the monitor at (0,0).
+- The launcher passes its foreground right to the game
+  (`AllowSetForegroundWindow`).
+
+Verified 2026-10-31 by automated runs: started without focus the game keeps
+loading in the background; with focus it reaches the main menu, survives
+switching to another window for 6 s and back, and quits cleanly on a close
+request (no crash report, `MemLeaks_sacred2.xml` written).
+
+## Consequences
+
+- The resolution and fullscreen settings in Optionen no longer apply; the
+  game always renders at the monitor's resolution.
+- Always the primary monitor.
+- In windowed mode the game presents with vsync (interval default); the
+  options' vsync flag only applies to exclusive fullscreen.